[Notifications Engine] Guard "this"

On teardown with the popup expanded, the cleanup handler might fire with us already having been deleted.

BUG: 397105
FIXED-IN: 5.12.7

Differential Revision: https://phabricator.kde.org/D14651

dataengines/notifications/notificationsengine.cpp

@@ -423,8 +423,11 @@ QSharedPointer<NotificationInhibiton> NotificationsEngine::createInhibition(cons
     ni->hint = hint;
     ni->value = value;
 
-    QSharedPointer<NotificationInhibiton> rc(ni, [this](NotificationInhibiton *ni) {
-        m_inhibitions.removeOne(ni);
+    QPointer<NotificationsEngine> guard(this);
+    QSharedPointer<NotificationInhibiton> rc(ni, [this, guard](NotificationInhibiton *ni) {
+        if (guard) {
+            m_inhibitions.removeOne(ni);
+        }
         delete ni;
     });
     m_inhibitions.append(ni);