lavf/utils: avoid using programs for duration when there's only one

This allows us to be more selective about the streams we derive durations from
(specifically, ignoring text streams with outlier end times) in the common case

libavformat/utils.c

@@ -2582,7 +2582,7 @@ static void update_stream_timings(AVFormatContext *ic)
     if (start_time != INT64_MAX) {
         ic->start_time = start_time;
         if (end_time != INT64_MIN) {
-            if (ic->nb_programs) {
+            if (ic->nb_programs > 1) {
                 for (i = 0; i < ic->nb_programs; i++) {
                     p = ic->programs[i];
                     if (p->start_time != AV_NOPTS_VALUE && p->end_time > p->start_time)