Qt: correctly handle mousewheel in selector

Close #6812
(cherry picked from commit 16c1b2916cf36a8e9c218ab856a62f289f6d2d80)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/gui/qt4/components/playlist/selector.cpp

@@ -31,6 +31,7 @@
 #include "playlist_model.hpp"                /* plMimeData */
 #include "input_manager.hpp"                 /* MainInputManager, for podcast */
 
+#include <QApplication>
 #include <QInputDialog>
 #include <QMessageBox>
 #include <QMimeData>
@@ -39,6 +40,7 @@
 #include <QHBoxLayout>
 #include <QPainter>
 #include <QPalette>
+#include <QScrollBar>
 
 #include <vlc_playlist.h>
 #include <vlc_services_discovery.h>
@@ -550,6 +552,12 @@ int PLSelector::getCurrentItemCategory()
 
 void PLSelector::wheelEvent( QWheelEvent *e )
 {
+    if( verticalScrollBar()->isVisible() && (
+        (verticalScrollBar()->value() != verticalScrollBar()->minimum() && e->delta() >= 0 ) ||
+        (verticalScrollBar()->value() != verticalScrollBar()->maximum() && e->delta() < 0 )
+        ) )
+        QApplication::sendEvent(verticalScrollBar(), e);
+
     // Accept this event in order to prevent unwanted volume up/down changes
     e->accept();
 }