Fix empty editor windows (#7515)

Fix the problem with empty windows as described in issue #7412.

The `refocus` method in `MainWindow` is made public so that it can be called from `Editor::closeEvent`. It has also been refactored for better readability.

---------

Co-authored-by: Michael Gregorius <michael.gregorius.git@arcor.de>
Co-authored-by: Dalton Messmer <messmer.dalton@gmail.com>

include/Editor.h

@@ -56,7 +56,7 @@ protected:
 	DropToolBar * addDropToolBar(Qt::ToolBarArea whereToAdd, QString const & windowTitle);
 	DropToolBar * addDropToolBar(QWidget * parent, Qt::ToolBarArea whereToAdd, QString const & windowTitle);
 
-	void closeEvent( QCloseEvent * _ce ) override;
+	void closeEvent(QCloseEvent * event) override;
 protected slots:
 	virtual void play() {}
 	virtual void record() {}

include/MainWindow.h

@@ -72,6 +72,8 @@ public:
 	LMMS_EXPORT SubWindow* addWindowedWidget(QWidget *w, Qt::WindowFlags windowFlags = QFlag(0));
 
 
+	void refocus();
+
 	///
 	/// \brief	Asks whether changes made to the project are to be saved.
 	///
@@ -195,7 +197,6 @@ private:
 	void finalize();
 
 	void toggleWindow( QWidget *window, bool forceShow = false );
-	void refocus();
 
 	void exportProject(bool multiExport = false);
 	void handleSaveResult(QString const & filename, bool songSavedSuccessfully);