ZMBV encoder forgot to fill coded frame pointer

Originally committed as revision 15359 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/zmbvenc.c

@@ -300,6 +300,8 @@ static av_cold int encode_init(AVCodecContext *avctx)
         return -1;
     }
 
+    avctx->coded_frame = (AVFrame*)&c->pic;
+
     return 0;
 }