sub: update subtitles if current track is an image

Any track that has attached picture is also always considered an image.
Not every image is neccesarily an attached picture though. So change the
check here to capture more possible cases where we should be updating
the subtitle. With the previous commits, this fixes mpv-player#12387.

player/sub.c

@@ -116,7 +116,7 @@ static bool update_subtitle(struct MPContext *mpctx, double video_pts,
     if (mpctx->video_out && mpctx->video_status == STATUS_EOF &&
         (mpctx->opts->subs_rend->sub_past_video_end ||
          !mpctx->current_track[0][STREAM_VIDEO] ||
-         mpctx->current_track[0][STREAM_VIDEO]->attached_picture)) {
+         mpctx->current_track[0][STREAM_VIDEO]->image)) {
         if (osd_get_force_video_pts(mpctx->osd) != video_pts) {
             osd_set_force_video_pts(mpctx->osd, video_pts);
             osd_query_and_reset_want_redraw(mpctx->osd);