libavcodec/vp8dsp.c:169: error: Uninitialized Value
  The value read from q0 was never initialized.

libavcodec/vp8dsp.c:169:5: 
167.     const uint8_t *cm = ff_crop_tab + MAX_NEG_CROP;
168. 
169.     a = 3 * (q0 - p0);
         ^
170. 
171.     if (is4tap)
