Make sure that m_selectionToggle is not 0 before calling deleteLater()

Commit 1938ad54d4 replaced delete by
deleteLater(). However, the latter cannot be used safely with null
pointers. This commit adds a safety check in order to make sure that
we do not get a crash.

Thanks to Christoph Feck for pointing out this issue.

src/kitemviews/kitemlistwidget.cpp

@@ -473,7 +473,7 @@ qreal KItemListWidget::hoverOpacity() const
 
 void KItemListWidget::slotHoverAnimationFinished()
 {
-    if (!m_hovered) {
+    if (!m_hovered && m_selectionToggle) {
         m_selectionToggle->deleteLater();
         m_selectionToggle = 0;
     }