Catch KeyError when checking mode from PNG IHDR chunk

[radarhere]

Pillow/src/PIL/PngImagePlugin.py

Lines 462 to 465 in 7e4ca8b

	try:
	self.im_mode, self.im_rawmode = _MODES[(s[8], s[9])]
	except Exception:
	pass

Exception can be made more specific. It is a KeyError that will be raised if the bit depth / color type combination doesn't have a match.

If you're concerned that s might not be long enough for s[9], the length has been checked a few lines earlier.

Pillow/src/PIL/PngImagePlugin.py

Lines 455 to 458 in 7e4ca8b

	s = ImageFile._safe_read(self.fp, length)
	if length < 13:
	if ImageFile.LOAD_TRUNCATED_IMAGES:
	return s