libavcodec/pngdec.c:236: error: Uninitialized Value
  The value read from b was never initialized.

libavcodec/pngdec.c:236:9: 
234.         }
235. #define OP_AVG(x, s, l) (((x + l) >> 1) + s) & 0xff
236.         UNROLL_FILTER(OP_AVG);
             ^
237.         break;
238.     case PNG_FILTER_VALUE_PAETH:
