Fix crash in EditorPropertyArray

(cherry picked from commit d80a2a89f07dfddc734c18ac8f565b968eb789c8)

editor/editor_properties_array_dict.cpp

@@ -675,6 +675,8 @@ void EditorPropertyArray::_reorder_button_up() {
 	reorder_mouse_y_delta = 0.0f;
 
 	Input::get_singleton()->set_mouse_mode(Input::MOUSE_MODE_VISIBLE);
+
+	ERR_FAIL_NULL(reorder_selected_button);
 	reorder_selected_button->warp_mouse(reorder_selected_button->get_size() / 2.0f);
 
 	reorder_selected_element_hbox = nullptr;