Fix TileMap error msg when optional navigation node is not set

Fixes TileMap error msg spam when bake_navigation=true but the optional and depr navigation node is not set.

scene/2d/tile_map.cpp

@@ -157,7 +157,11 @@ void TileMap::_update_quadrant_transform() {
 
 	Transform2D nav_rel;
 	if (bake_navigation) {
-		nav_rel = get_relative_transform_to_parent(navigation);
+		if (navigation) {
+			nav_rel = get_relative_transform_to_parent(navigation);
+		} else {
+			nav_rel = get_transform();
+		}
 	}
 
 	for (Map<PosKey, Quadrant>::Element *E = quadrant_map.front(); E; E = E->next()) {
@@ -339,7 +343,11 @@ void TileMap::update_dirty_quadrants() {
 	Vector2 tofs = get_cell_draw_offset();
 	Transform2D nav_rel;
 	if (bake_navigation) {
-		nav_rel = get_relative_transform_to_parent(navigation);
+		if (navigation) {
+			nav_rel = get_relative_transform_to_parent(navigation);
+		} else {
+			nav_rel = get_transform();
+		}
 	}
 
 	Vector2 qofs;