LibGUI: Hide ResizeCorner in StatusBar when window is maximized

Fully expands status bars when maximized and prevents maximized
windows from being erroneously resized.

Libraries/LibGUI/StatusBar.h

@@ -43,6 +43,7 @@ public:
 protected:
     explicit StatusBar(int label_count = 1);
     virtual void paint_event(PaintEvent&) override;
+    virtual void resize_event(ResizeEvent&) override;
 
 private:
     NonnullRefPtr<Label> create_label();