Only emit empty() in SessionFinished() when in TabbedNavigation mode

empty() is emitted so that MainWindow calls close() and we get rid of the
colours-flashing bug when closing the last session/tab in a window, see
commit bbec72250d. However all that isn't relevant when we are in
konsole Part mode, where there are no tabs or MainWindows.

This fixes a crash in Dolphin when closing its window while the embedded
Konsole Part is open. The crash would happen as calling
ViewContainer::currentTabViewCount() would end up in the ViewSplitter code
path, which is no-op in Konsole Part.

To test:
- Open dolphin, make sure the terminal panel isn't open to begin with
- open the terminal panel
- close the dolphin window while the terminal panel is open

BUG: 441206
FIXED-IN: 21.08.1

src/ViewManager.cpp

@@ -494,11 +494,13 @@ void ViewManager::sessionFinished()
         return;
     }
 
-    // The last session/tab, and only one view (no splits), emit empty()
-    // so that close() is called in MainWindow, fixes #432077
-    if (_viewContainer->count() == 1 && _viewContainer->currentTabViewCount() == 1) {
-        Q_EMIT empty();
-        return;
+    if (_navigationMethod == TabbedNavigation) {
+        // The last session/tab, and only one view (no splits), emit empty()
+        // so that close() is called in MainWindow, fixes #432077
+        if (_viewContainer->count() == 1 && _viewContainer->currentTabViewCount() == 1) {
+            Q_EMIT empty();
+            return;
+        }
     }
 
     auto *session = qobject_cast<Session *>(sender());