pause if preferences dialog is open, fixes #413

dialogs/preferencesdialog.h

@@ -31,7 +31,7 @@ class PreferencesDialog : public QDialog
 	Q_OBJECT
 
 public:
-	explicit PreferencesDialog(QWidget *parent = 0);
+	explicit PreferencesDialog(QWidget *parent = nullptr);
 	~PreferencesDialog();
 
 	void setup_kbd_shortcuts(QMenuBar* menu);

mainwindow.cpp

@@ -1239,8 +1239,10 @@ void MainWindow::maximize_panel() {
 	}
 }
 
-void MainWindow::preferences()
-{
+void MainWindow::preferences() {
+	panel_sequence_viewer->pause();
+	panel_footage_viewer->pause();
+
 	PreferencesDialog pd(this);
 	pd.setup_kbd_shortcuts(menuBar());
 	pd.exec();