Port away from deprecated QWheelEvent::delta()

QWheelEvent::angleDelta() returns a QPoint instead of int, so we need to
use its y() value to get the number of steps.

src/views/dolphinview.cpp

@@ -847,10 +847,10 @@ bool DolphinView::eventFilter(QObject* watched, QEvent* event)
 void DolphinView::wheelEvent(QWheelEvent* event)
 {
     if (event->modifiers().testFlag(Qt::ControlModifier)) {
-        const int numDegrees = event->delta() / 8;
-        const int numSteps = numDegrees / 15;
+        const QPoint numDegrees = event->angleDelta() / 8;
+        const QPoint numSteps = numDegrees / 15;
 
-        setZoomLevel(zoomLevel() + numSteps);
+        setZoomLevel(zoomLevel() + numSteps.y());
         event->accept();
     } else {
         event->ignore();