Allow Center Selection to work without any selection in 2D/3D editors

When there is no selection, the camera will center around the
world origin.

This helps people get back to the world center if they haven't added
any nodes yet.

(cherry picked from commit fc055e1993)

editor/plugins/spatial_editor_plugin.cpp

@@ -3473,9 +3473,6 @@ void SpatialEditorViewport::reset() {
 }
 
 void SpatialEditorViewport::focus_selection() {
-	if (!get_selected_count())
-		return;
-
 	Vector3 center;
 	int count = 0;