avplay: Don't try to scale timestamps if the tb isn't set

If get_filtered_video_frame failed above, tb might not be
initialized at all, so don't scale using it.

This fixes cases where avplay could crash if aborting
avformat_find_stream_info with ctrl+c.
Signed-off-by: Martin Storsjö <martin@martin.st>

avplay.c

@@ -1796,7 +1796,7 @@ static int video_thread(void *arg)
             frame->opaque = picref;
         }
 
-        if (av_cmp_q(tb, is->video_st->time_base)) {
+        if (ret >= 0 && av_cmp_q(tb, is->video_st->time_base)) {
             av_unused int64_t pts1 = pts_int;
             pts_int = av_rescale_q(pts_int, tb, is->video_st->time_base);
             av_dlog(NULL, "video_thread(): "