Temporarily removes agent from navigation map when parent node cannot process due to SceneTree pause and process_mode property. Normal process_mode does not work as other agents would still avoid the paused agents because they were still active on the navigation map and the rvo world. Also fixes potential crash when region_get_map or agent_get_map is called while no map is set.
(cherry picked from commit 6b51ab66d8)
88acb5b798