filters.python produces broken metadata when 2 or more files processed

When running pdal pipeline with filters.python inside and requesting metadata output is broken by unquoted string values.

Example pipeline:

[
  {
    "type": "readers.las",
    "filename": "1.2-with-color.las"
  },
  {
    "type": "readers.las",
    "filename": "1.2-with-color.las"
  },
  {
    "type": "filters.python",
    "source": "def foo(ins, outs):\n    return True",
    "module": "anything",
    "function": "foo"
  },
  {
    "type": "writers.las",
    "filename": "/tmp/out.laz"
  }
]

Run:

pdal -v 8 pipeline --metadata m.json pl.json 

(PDAL Debug) Debugging...
(pdal pipeline Debug) Attempting to load plugin '/home/bacek/miniconda3/envs/pdal-clean/lib/python3.8/site-packages/lib/libpdal_plugin_filter_python.so'.
(pdal pipeline Debug) Loaded plugin '/home/bacek/miniconda3/envs/pdal-clean/lib/python3.8/site-packages/lib/libpdal_plugin_filter_python.so'.
(pdal pipeline Debug) Initialized plugin '/home/bacek/miniconda3/envs/pdal-clean/lib/python3.8/site-packages/lib/libpdal_plugin_filter_python.so'.
(pdal pipeline Debug) Executing pipeline in standard mode.
(pdal pipeline filters.python Debug)                    filters.python source=[35 bytes], module=anything, function=foo
 processing 1065 points.
(pdal pipeline filters.python Debug)                    filters.python source=[35 bytes], module=anything, function=foo
 processing 1065 points.
(pdal pipeline writers.las Debug) Wrote 2130 points to the LAS file

Generated metadata:

{
  "stages":
  {
    "filters.python":
    {
      "creation_doy":
      [
        0,
        0
      ],
      "creation_year":
      [
        0,
        0
      ],
      "dataformat_id":
      [
        3,
        3
      ],
      "filesource_id":
      [
        0,
        0
      ],
      "filters.python":
      {
      },
      "global_encoding":
      [
        0,
        0
      ],
      "major_version":
      [
        1,
        1
      ],
      "minor_version":
      [
        2,
        2
      ],
      "offset_x":
      [
        0,
        0
      ],
      "offset_y":
      [
        0,
        0
      ],
      "offset_z":
      [
        0,
        0
      ],
      "project_id":
      [
        00000000-0000-0000-0000-000000000000,
        00000000-0000-0000-0000-000000000000
      ],
      "readers.las":
      [
        {
        },
        {
        },
        {
        },
        {
        }
      ],
      "root":
      [
        {
        },
        {
        }
      ],
      "scale_x":
      [
        0.01,
        0.01
      ],
      "scale_y":
      [
        0.01,
        0.01
      ],
      "scale_z":
      [
        0.01,
        0.01
      ],
      "software_id":
      [
        TerraScan,
        TerraScan
      ],
      "srs":
      [
        {
        },
        {
        },
        {
        },
        {
        }
      ],
      "system_id":
      [
        {
        },
        {
        }
      ],
      "units":
      [
        {
        },
        {
        },
        {
        },
        {
        }
      ]
    },
    "readers.las":
    [
      {
        "comp_spatialreference": "",
        "compressed": false,
        "count": 1065,
        "creation_doy": 0,
        "creation_doy":         {
          "temp": 0
        },
        "creation_year": 0,
        "creation_year":         {
          "temp": 0
        },
        "dataformat_id": 3,
        "dataformat_id":         {
          "temp": 3
        },
        "dataoffset": 229,
        "filesource_id": 0,
        "filesource_id":         {
          "temp": 0
        },
        "global_encoding": 0,
        "global_encoding":         {
          "temp": 0
        },
        "global_encoding_base64": "AAA=",
        "header_size": 227,
        "major_version": 1,
        "major_version":         {
          "temp": 1
        },
        "maxx": 638982.55,
        "maxy": 853535.43,
        "maxz": 586.38,
        "minor_version": 2,
        "minor_version":         {
          "temp": 2
        },
        "minx": 635619.85,
        "miny": 848899.7,
        "minz": 406.59,
        "offset_x": 0,
        "offset_x":         {
          "temp": 0
        },
        "offset_y": 0,
        "offset_y":         {
          "temp": 0
        },
        "offset_z": 0,
        "offset_z":         {
          "temp": 0
        },
        "point_length": 34,
        "project_id": "00000000-0000-0000-0000-000000000000",
        "project_id":         {
          "temp": "00000000-0000-0000-0000-000000000000"
        },
        "scale_x": 0.01,
        "scale_x":         {
          "temp": 0.01
        },
        "scale_y": 0.01,
        "scale_y":         {
          "temp": 0.01
        },
        "scale_z": 0.01,
        "scale_z":         {
          "temp": 0.01
        },
        "software_id": "TerraScan",
        "software_id":         {
          "temp": "TerraScan"
        },
        "spatialreference": "",
        "srs":
        {
          "compoundwkt": "",
          "horizontal": "",
          "isgeocentric": false,
          "isgeographic": false,
          "prettycompoundwkt": "",
          "prettywkt": "",
          "proj4": "",
          "units":
          {
            "horizontal": "unknown",
            "vertical": ""
          },
          "vertical": "",
          "wkt": ""
        },
        "system_id": "",
        "system_id":         {
          "temp": ""
        }
      },
      {
        "comp_spatialreference": "",
        "compressed": false,
        "count": 1065,
        "creation_doy": 0,
        "creation_year": 0,
        "dataformat_id": 3,
        "dataoffset": 229,
        "filesource_id": 0,
        "global_encoding": 0,
        "global_encoding_base64": "AAA=",
        "header_size": 227,
        "major_version": 1,
        "maxx": 638982.55,
        "maxy": 853535.43,
        "maxz": 586.38,
        "minor_version": 2,
        "minx": 635619.85,
        "miny": 848899.7,
        "minz": 406.59,
        "offset_x": 0,
        "offset_y": 0,
        "offset_z": 0,
        "point_length": 34,
        "project_id": "00000000-0000-0000-0000-000000000000",
        "scale_x": 0.01,
        "scale_y": 0.01,
        "scale_z": 0.01,
        "software_id": "TerraScan",
        "spatialreference": "",
        "srs":
        {
          "compoundwkt": "",
          "horizontal": "",
          "isgeocentric": false,
          "isgeographic": false,
          "prettycompoundwkt": "",
          "prettywkt": "",
          "proj4": "",
          "units":
          {
            "horizontal": "unknown",
            "vertical": ""
          },
          "vertical": "",
          "wkt": ""
        },
        "system_id": ""
      }
    ],
    "writers.las":
    {
      "filename":
      [
        "/tmp/out.laz"
      ]
    }
  }
}

stages/filters.python has unquoted strings in project_id and sotfware_id.

PDAL / python

filters.python produces broken metadata when 2 or more files processed #87