[TechDraw] prevent crash where user duplicates page without also duplicating dependencies

src/Mod/TechDraw/App/DrawView.cpp

@@ -239,6 +239,26 @@ void DrawView::onDocumentRestored()
     handleXYLock();
     DrawView::execute();
 }
+/**
+ * @brief DrawView::countParentPages
+ * Fixes a crash in TechDraw when user creates duplicate page without dependencies
+ * In fixOrphans() we check how many parent pages an object has before deleting
+ * in case it is also a child of another duplicate page
+ * @return
+ */
+int DrawView::countParentPages() const
+{
+    int count = 0;
+
+    std::vector<App::DocumentObject*> parent = getInList();
+    for (std::vector<App::DocumentObject*>::iterator it = parent.begin(); it != parent.end(); ++it) {
+        if ((*it)->getTypeId().isDerivedFrom(DrawPage::getClassTypeId())) {
+            //page = static_cast<TechDraw::DrawPage *>(*it);
+            count++;
+        }
+    }
+    return count;
+}
 
 DrawPage* DrawView::findParentPage() const
 {

src/Mod/TechDraw/App/DrawView.h

@@ -85,6 +85,7 @@ public:
     virtual PyObject *getPyObject(void) override;
 
     virtual DrawPage* findParentPage() const;
+    virtual int countParentPages() const;
     virtual QRectF getRect() const;                      //must be overridden by derived class
     virtual double autoScale(void) const;
     virtual double autoScale(double w, double h) const;

src/Mod/TechDraw/Gui/MDIViewPage.cpp

@@ -481,7 +481,11 @@ void MDIViewPage::fixOrphans(bool force)
             m_view->removeQView(qv);
         } else {
             TechDraw::DrawPage* pp = qv->getViewObject()->findParentPage();
-            if (thisPage != pp) {
+            /** avoid crash where a view might have more than one parent page
+             * if the user duplicated the page without duplicating dependencies
+             */
+            int numParentPages = qv->getViewObject()->countParentPages();
+            if (thisPage != pp && numParentPages == 1) {
                m_view->removeQView(qv);
             }
         }