H264: Fix decoding with CABAC/delta_qp/PCM macroblocks.

Patch by Jason Garrett-Glaser (darkshikari gmail com)

Originally committed as revision 14160 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h264.c

@@ -5746,6 +5746,7 @@ decode_intra_mb:
         // All coeffs are present
         memset(h->non_zero_count[mb_xy], 16, 16);
         s->current_picture.mb_type[mb_xy]= mb_type;
+        h->last_qscale_diff = 0;
         return 0;
     }