fixing uninitalized dc_pred_dir

this needs testing (no files with intra_dc_threshold and vissible ac_pred errors here)

Originally committed as revision 5137 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h263.c

@@ -4756,6 +4756,7 @@ static inline int mpeg4_decode_block(MpegEncContext * s, DCTELEM * block,
         i = 0;
       }else{
             i = -1;
+            ff_mpeg4_pred_dc(s, n, 0, &dc_pred_dir, 0);
       }
         if (!coded)
             goto not_coded;