libavcodec/pngdec.c:224: error: Uninitialized Value
  The value read from g was never initialized.

libavcodec/pngdec.c:224:13: 
222.         } else {
223. #define OP_SUB(x, s, l) x + s
224.             UNROLL_FILTER(OP_SUB);
                 ^
225.         }
226.         break;
