The decoder was requiring GIF files to be at least 32 bytes, but the
actual minimum for a valid GIF is only 26 bytes:
- 6 bytes for the header
- 7 bytes for the Logical Screen Descriptor
- 10 bytes for the Image Descriptor
- 2 bytes for the LZW minimum code size and block terminator
- 1 byte for the GIF trailer
This change allows us to load minimal 1x1 GIFs with empty LZW data.
They are commonly used on the web as transparent placeholders with
minimal file size.
GIF loader was completely failing when encountering errors with
frame descriptors or individual frames, even when some frames were
successfully loaded. Now we attempt to decode at least some frames
and fail only when no frames can be decoded at all.
