Gui: fix several regressions caused by PR #12035

* fix hard crash in MainWindow::_updateActions() if no MDI view exists
* in MDIView::buildWindowTitle() use the label of the document because this changes when saving it while the name is immutable
* fix const correctness in MDIView::buildWindowTitle()
* do not set the modified flag of the main window in MDIView::buildWindowTitle() but in the calling instance
* move setting the main window title to Application::viewActivated to reduce code duplication
* fix missing application name if FreeCADGui is loaded as Python module

src/Gui/Application.cpp

@@ -1260,6 +1260,10 @@ void Application::viewActivated(MDIView* pcView)
 #endif
 
     signalActivateView(pcView);
+    getMainWindow()->setWindowTitle(pcView->buildWindowTitle());
+    if (auto document = pcView->getGuiDocument()) {
+        getMainWindow()->setWindowModified(document->isModified());
+    }
 
     // Set the new active document which is taken of the activated view. If, however,
     // this view is passive we let the currently active document unchanged as we would

src/Gui/MDIView.cpp

@@ -448,18 +448,11 @@ void MDIView::setCurrentViewMode(ViewMode mode)
     }
 }
 
-QString MDIView::buildWindowTitle()
+QString MDIView::buildWindowTitle() const
 {
     QString windowTitle;
     if (Gui::Document* document = getGuiDocument()) {
-        if (document->isModified()) {
-            getMainWindow()->setWindowModified(TRUE);
-        }
-        else {
-            getMainWindow()->setWindowModified(FALSE);
-        }
-
-        windowTitle.append(QString::fromUtf8(getAppDocument()->getName()));
+        windowTitle.append(QString::fromStdString(getAppDocument()->Label.getStrValue()));
     }
 
     return windowTitle;

src/Gui/MDIView.h

@@ -75,7 +75,7 @@ public:
     virtual void viewAll();
 
     /// build window title
-    QString buildWindowTitle();
+    QString buildWindowTitle() const;
 
     /// Message handler
     bool onMsg(const char* pMsg,const char** ppReturn) override;

src/Gui/MainWindow.cpp

@@ -1268,9 +1268,8 @@ void MainWindow::removeWindow(Gui::MDIView* view, bool close)
 
 void MainWindow::tabChanged(MDIView* view)
 {
-    Q_UNUSED(view);
+    Q_UNUSED(view)
     updateActions();
-    getMainWindow()->setWindowTitle(view->buildWindowTitle());
 }
 
 void MainWindow::tabCloseRequested(int index)
@@ -1665,8 +1664,15 @@ void MainWindow::_updateActions()
         d->activityTimer->stop();
         Application::Instance->commandManager().testActive();
     }
+
     d->actionUpdateDelay = 0;
-    getMainWindow()->setWindowTitle(activeWindow()->buildWindowTitle());
+
+    if (auto view = activeWindow()) {
+        setWindowTitle(view->buildWindowTitle());
+        if (auto document = view->getGuiDocument()) {
+            setWindowModified(document->isModified());
+        }
+    }
 }
 
 void MainWindow::updateEditorActions()
@@ -2370,7 +2376,6 @@ void MainWindow::changeEvent(QEvent *e)
                     d->activeView = view;
                     Application::Instance->viewActivated(view);
                 }
-                getMainWindow()->setWindowTitle(view->buildWindowTitle());
             }
         }
     }
@@ -2515,8 +2520,10 @@ QMdiArea *MainWindow::getMdiArea() const
 void MainWindow::setWindowTitle(const QString& string)
 {
     QString title;
-    QString appname =
-        QString(static_cast<QApplication*>(QCoreApplication::instance())->applicationName());
+    QString appname = QCoreApplication::applicationName();
+    if (appname.isEmpty()) {
+        appname = QString::fromLatin1(App::Application::Config()["ExeName"].c_str());
+    }
 
     // allow to disable version number
     ParameterGrp::handle hGen = +App::GetApplication().GetParameterGroupByPath(