Merge pull request #73252 from smix8/navigationserver_improve_rid_not_found_error_4.x

Improve NavigationServer.free() error msg when RID not found

modules/navigation/godot_navigation_server.cpp

@@ -757,7 +757,7 @@ COMMAND_1(free, RID, p_object) {
 		agent_owner.free(p_object);
 
 	} else {
-		ERR_FAIL_COND("Invalid ID.");
+		ERR_FAIL_COND("Attempted to free a NavigationServer RID that did not exist (or was already freed).");
 	}
 }