ffplay: only drop frames if not in frame step mode

Fixes ticket #2053.
Signed-off-by: Marton Balint <cus@passwd.hu>

ffplay.c

@@ -1339,7 +1339,7 @@ retry:
             if (is->pictq_size > 1) {
                 VideoPicture *nextvp = &is->pictq[(is->pictq_rindex + 1) % VIDEO_PICTURE_QUEUE_SIZE];
                 duration = nextvp->pts - vp->pts;
-                if((framedrop>0 || (framedrop && get_master_sync_type(is) != AV_SYNC_VIDEO_MASTER)) && time > is->frame_timer + duration){
+                if(!is->step && (framedrop>0 || (framedrop && get_master_sync_type(is) != AV_SYNC_VIDEO_MASTER)) && time > is->frame_timer + duration){
                     is->frame_drops_late++;
                     pictq_next_picture(is);
                     goto retry;