Qt: preferences: use QSplitter for advanced layout base

modules/gui/qt4/dialogs/preferences.cpp

@@ -42,6 +42,7 @@
 #include <QMessageBox>
 #include <QDialogButtonBox>
 #include <QStackedWidget>
+#include <QSplitter>
 
 PrefsDialog::PrefsDialog( QWidget *parent, intf_thread_t *_p_intf )
             : QVLCDialog( parent, _p_intf )
@@ -97,7 +98,7 @@ PrefsDialog::PrefsDialog( QWidget *parent, intf_thread_t *_p_intf )
     simple_split_widget = new QWidget();
     simple_split_widget->setLayout( new QHBoxLayout );
 
-    advanced_split_widget = new QWidget();
+    advanced_split_widget = new QSplitter();
     advanced_split_widget->setLayout( new QHBoxLayout );
 
     stack = new QStackedWidget();

modules/gui/qt4/dialogs/preferences.hpp

@@ -40,6 +40,7 @@ class QCheckBox;
 class QLabel;
 class SearchLineEdit;
 class QStackedWidget;
+class QSplitter;
 
 class PrefsDialog : public QVLCDialog
 {
@@ -56,7 +57,8 @@ private:
     enum { SIMPLE, ADVANCED };
     QStackedWidget *stack;
 
-    QWidget *simple_split_widget, *advanced_split_widget;
+    QWidget *simple_split_widget;
+    QSplitter *advanced_split_widget;
 
     QStackedWidget *advanced_panels_stack;
     QStackedWidget *simple_panels_stack;