FS-11573 fix seg when missing conference layout config

src/mod/applications/mod_conference/conference_video.c

@@ -2031,6 +2031,8 @@ video_layout_t *conference_video_get_layout(conference_obj_t *conference, const
 	layout_group_t *lg = NULL;
 	video_layout_t *vlayout = NULL;
 
+	if (!video_layout_name) return NULL;
+
 	if (video_layout_group) {
 		lg = switch_core_hash_find(conference->layout_group_hash, video_layout_group);
 		vlayout = conference_video_find_best_layout(conference, lg, 0, 0);