Fix segfault due to deallocated entries in delayed_pic after size change.

Fixes issue714.

Originally committed as revision 15965 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h264.c

@@ -3639,6 +3639,7 @@ static int decode_slice_header(H264Context *h, H264Context *h0){
         if(h != h0)
             return -1;   // width / height changed during parallelized decoding
         free_tables(h);
+        flush_dpb(s->avctx);
         MPV_common_end(s);
     }
     if (!s->context_initialized) {