Image export crash when font string includes quoted font family

[jonmmease]

When a font specification includes a font family quoted in double quotes, image export crashes the Python kernel.

import vl_convert as vlc
spec = {
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "layer": [
    {
      "data": {
        "name": "df",
        "values": [{"a": 1, "b": 1}, {"a": 2, "b": 3}, {"a": 3, "b": 2}]
      },
      "layer": [
        {
          "transform": [],
          "layer": [
            {
              "mark": {"type": "line"},
            }
          ],
          "encoding": {
            "x": {
              "field": "a",
              "type": "quantitative"
            },
            "y": {
              "field": "b",
              "type": "quantitative"
            },
          }
        }
      ]
    }
  ],
  "config": {
    "style": {
      "guide-label": {
        "font": "Arial, sans-serif"
      },
      "guide-title": {
        "font": "Arial, sans-serif"
      }
    }
  }
}

# Works ok
svg = vlc.vegalite_to_svg(spec)

# Update font strings to quote Arial. Crashes kernel
spec["config"]["style"]["guide-label"]["font"] = "\"Arial\", sans-serif"
spec["config"]["style"]["guide-label"]["font"] = "\"Arial\", sans-serif"
svg = vlc.vegalite_to_svg(spec)

A little more info in the stack trace is available when running the example in Rust:

thread '<unnamed>' panicked at 'Failed to parse text SVG: ParsingFailed(ParserError(InvalidAttribute(InvalidSpace(73, TextPos { row: 3, col: 54 }), TextPos { row: 3, col: 54 })))', vl-convert-rs/src/text.rs:187:59
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
fatal runtime error: failed to initiate panic, error 5
Fatal Python error: Aborted

The first thing we should do is update error handling to not panic and crash the kernel on SVG parse failure. Then we should fix the bug 😄