Part: [skip ci] fix crash when closing document while face colors panel is open

src/Gui/Selection.cpp

@@ -972,11 +972,14 @@ void SelectionSingleton::rmvSelectionGate(void)
 {
     if (ActiveGate) {
         delete ActiveGate;
-        ActiveGate=0;
+        ActiveGate = nullptr;
+
         Gui::Document* doc = Gui::Application::Instance->activeDocument();
         if (doc) {
+            // if a document is about to be closed it has no MDI view any more
             Gui::MDIView* mdi = doc->getActiveView();
-            mdi->restoreOverrideCursor();
+            if (mdi)
+                mdi->restoreOverrideCursor();
         }
     }
 }

src/Mod/Part/Gui/TaskFaceColors.cpp

@@ -34,6 +34,7 @@
 # include <TopTools_IndexedMapOfShape.hxx>
 # include <QFontMetrics>
 # include <QMessageBox>
+# include <QPointer>
 # include <QSet>
 # include <Python.h>
 # include <Inventor/SoPickedPoint.h>
@@ -97,7 +98,7 @@ class FaceColors::Private
 public:
     typedef boost::signals2::connection Connection;
     Ui_TaskFaceColors* ui;
-    Gui::View3DInventorViewer* view;
+    QPointer<Gui::View3DInventorViewer> view;
     ViewProviderPartExt* vp;
     App::DocumentObject* obj;
     Gui::Document* doc;