QGIS crashes for invalid filepaths

[noerw]

The plugin causes QGIS to crash when incorrect paths are provided in the 'File' option:

• crash when existing file is selected
• crash when no file extension is provided
• no crash when nonexistent file ending in .mbtiles is selected

My request is to..

• catch these errors, providing helpful error messages
• improve the interface to select output file
  • browse button, autocomplete file extension?

[simgislab]

Rendering hangs indefinitely when attempting to write NGRC to a folder that doesn't exist

!

In the example above 'qtiles' doesn't exist.