gif2webp: fix transcode of loop count=65535

with loop_compatibility disabled (the default), non-zero loop counts
will be incremented by 1 for browser rendering compatibility. the max,
65535, is a special case as the muxer will fail if it is exceeded; avoid
increasing the limit in this case. this isn't 100% correct, but should
be close enough given the high number of iterations.

BUG=webp:382

Change-Id: Icde3e98a58e9ee89604a72fafda30ab71060dec5

examples/anim_util.c

@@ -275,6 +275,7 @@ static int ReadAnimatedWebP(const char filename[],
     prev_frame_timestamp = timestamp;
   }
   ok = dump_ok;
+  if (ok) image->format = ANIM_WEBP;
 
  End:
   WebPAnimDecoderDelete(dec);
@@ -687,6 +688,7 @@ static int ReadAnimatedGIF(const char filename[], AnimatedImage* const image,
       }
     }
   }
+  image->format = ANIM_GIF;
   DGifCloseFile(gif, NULL);
   return 1;
 }