fixed issue with "empty" elements [walls, stairs, elevators] during tool selection

minor ui changes

mapview/2D/tools/ToolNewStair.h

@@ -14,17 +14,22 @@ private:
 public:
 
 	ToolNewStair(Tools& tools, MapLayer* layer) : ToolNewElement(tools, layer) {
-		create();
+		;
+	}
+
+	void becomesActive() override {
+		create();			// start adding an new element
+		emit onHelpTextChange("click for the stair's starting point");
+	}
+
+	void becomesInactive() override {
+		deleteCurrent();	// delete the currently pending and not yet finished stair
 	}
 
 	const std::string getName() const override {
 		return "new Stair";
 	}
 
-	void becomesActive() override {
-		emit onHelpTextChange("click for the stair's starting point");
-	}
-
 	void createEmptyElement() override {
 
 		foEL = new Floorplan::StairFreeform();