prevent writing empty stss atom

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@12636 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavformat/movenc.c

@@ -734,7 +734,7 @@ static int mov_write_stbl_tag(ByteIOContext *pb, MOVTrack* track)
     mov_write_stsd_tag(pb, track);
     mov_write_stts_tag(pb, track);
     if (track->enc->codec_type == CODEC_TYPE_VIDEO &&
-        track->hasKeyframes < track->entry)
+        track->hasKeyframes && track->hasKeyframes < track->entry)
         mov_write_stss_tag(pb, track);
     if (track->enc->codec_type == CODEC_TYPE_VIDEO &&
         track->hasBframes)