libavcodec/gif.c:109: error: Uninitialized Value
  The value read from len was never initialized.

libavcodec/gif.c:109:9: 
107.     ptr = buf;
108.     for (height = avctx->height; height--;) {
109.         len += ff_lzw_encode(s->lzw, ptr, avctx->width);
             ^
110.         ptr += linesize;
111.     }
