Proper condition in xvmc decode mb.

The old one would try to use mv blocks that are written outside their buffer,
in case of unhandled error.

Originally committed as revision 17315 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mpegvideo_xvmc.c

@@ -297,6 +297,6 @@ void ff_xvmc_decode_mb(MpegEncContext *s)
      * blocks. */
 
 
-    if (render->filled_mv_blocks_num >= render->total_number_of_mv_blocks)
+    if (render->filled_mv_blocks_num == render->total_number_of_mv_blocks)
         ff_draw_horiz_band(s, 0, 0);
 }