avformat/movenc: Fix stts_entries allocation check

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/movenc.c

@@ -1833,7 +1833,7 @@ static int mov_write_stts_tag(AVIOContext *pb, MOVTrack *track)
         stts_entries = track->entry ?
                        av_malloc_array(track->entry, sizeof(*stts_entries)) : /* worst case */
                        NULL;
-        if (!stts_entries)
+        if (track->entry && !stts_entries)
             return AVERROR(ENOMEM);
         for (i = 0; i < track->entry; i++) {
             int duration = get_cluster_duration(track, i);