Gdk-pixbuf: uninitialized memory disclosure in gdkpixbuf gif lzw decoder

A flaw was found in the GIF parser of GdkPixbuf’s LZW decoder. When an invalid symbol is encountered during decompression, the decoder sets the reported output size to the full buffer length rather than the actual number of written bytes. This logic error results in uninitialized sections of the buffer being included in the output, potentially leaking arbitrary memory contents in the processed image.