avformat/avidec: Speed up keyframe detection code

Fixes Ticket3531
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/avidec.c

@@ -1413,7 +1413,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
                 AVIndexEntry *e;
                 int index;
 
-                index = av_index_search_timestamp(st, ast->frame_offset, 0);
+                index = av_index_search_timestamp(st, ast->frame_offset, AVSEEK_FLAG_ANY);
                 e     = &st->index_entries[index];
 
                 if (index >= 0 && e->timestamp == ast->frame_offset) {