Fix crash in DrawViewDraft/DrawViewArch

- when restoring DVD/DVA from old files, convert Source from
  PropertyLinkGlobal to PropertyLink with Scope = Global. Note
  subtle difference from Restore method in DrawView - PropertyLink
  vs PropertyLinkList.

src/Mod/TechDraw/App/DrawViewDraft.h

@@ -61,6 +61,8 @@ public:
     virtual const char* getViewProviderName(void) const {
         return "TechDrawGui::ViewProviderDraft";
     }
+    void Restore(Base::XMLReader &reader) override;
+
 
 protected:
     virtual void onChanged(const App::Property* prop);