Fix crash when failing to restore session

REVIEW: 128670
BUG: 366217

src/ViewManager.cpp

@@ -941,6 +941,14 @@ void ViewManager::restoreSessions(const KConfigGroup& group)
     int tab = 1;
     foreach(int id, ids) {
         Session* session = SessionManager::instance()->idToSession(id);
+
+        if (!session) {
+            qWarning() << "Unable to load session with id" << id;
+            // Force a creation of a default session below
+            ids.clear();
+            break;
+        }
+
         createView(session);
         if (!session->isRunning())
             session->run();