empty "graphics" in JSON causes PIL error

[max-vogler]

If map.json has no graphics:

{
  "graphics": [],
  "objects": [],
  "tiles": ["collision"]
}

butano-tiled throws an error:

Traceback (most recent call last):
  File "/utano-tiled/bntmx.py", line 293, in <module>
    process(args.mapsdirs, args.build)
  File "butano-tiled/bntmx.py", line 267, in process
    gfx_im.save(bmp_filename, "BMP")
  File "/usr/local/lib/python3.11/site-packages/PIL/Image.py", line 2431, in save
    save_handler(self, fp, filename)
  File "/usr/local/lib/python3.11/site-packages/PIL/BmpImagePlugin.py", line 451, in _save
    ImageFile._save(im, fp, [("raw", (0, 0) + im.size, 0, (rawmode, stride, -1))])
  File "/usr/local/lib/python3.11/site-packages/PIL/ImageFile.py", line 520, in _save
    _encode_tile(im, fp, tile, bufsize, fh)
  File "/usr/local/lib/python3.11/site-packages/PIL/ImageFile.py", line 533, in _encode_tile
    encoder.setimage(im.im, b)
SystemError: tile cannot extend outside image
make: *** [all] Error 1