Do a little more checking.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@13502 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavformat/tiertexseq.c

@@ -110,7 +110,7 @@ static int seq_fill_buffer(SeqDemuxContext *seq, ByteIOContext *pb, int buffer_n
         return AVERROR_INVALIDDATA;
 
     seq_buffer = &seq->frame_buffers[buffer_num];
-    if (seq_buffer->fill_size + data_size > seq_buffer->data_size)
+    if (seq_buffer->fill_size + data_size > seq_buffer->data_size || data_size <= 0)
         return AVERROR_INVALIDDATA;
 
     url_fseek(pb, seq->current_frame_offs + data_offs, SEEK_SET);