navigator: check _navigation_mode_array before run

src/modules/navigator/navigator_main.cpp

@@ -710,8 +710,10 @@ Navigator::run()
 
 		/* iterate through navigation modes and set active/inactive for each */
 		for (unsigned int i = 0; i < NAVIGATOR_MODE_ARRAY_SIZE; i++) {
+			if (_navigation_mode_array[i]) {
 				_navigation_mode_array[i]->run(_navigation_mode == _navigation_mode_array[i]);
 			}
+		}
 
 		/* if nothing is running, set position setpoint triplet invalid once */
 		if (_navigation_mode == nullptr && !_pos_sp_triplet_published_invalid_once) {