#191 Fix integer overflows, out-of-bounds access, and uninitialized memory

[pandablackhole]

This patch fixes 7 memory safety issues across giflib:

1. gifalloc.c (GifUnionColorMap): Heap OOB read/write - CrntSlot guard + off-by-one fix
2. gifalloc.c (GifApplyTranslation): Integer overflow in Width*Height
3. gifalloc.c (GifMakeSavedImage): Integer overflow in raster allocation → heap buffer overflow
4. gifalloc.c (GifAddExtensionBlock): Uninitialized heap memory disclosure
5. egif_lib.c + dgif_lib.c: Signed integer overflow in PixelCount on 32-bit
6. egif_lib.c (EGifSpew): Signed overflow in row pointer arithmetic
7. quantize.c (GifQuantizeBuffer): Stack buffer overflow + Width*Height overflow

[Ildar Mulyukov]

the patch is very strange. Could you please clarify how is it supposed to be applied?

Note: it patches files like vp8/encoder/onyx_if.c