Fix crash when using box selection with Arch Survey

doSelect() loops over document's object vector.  It can happen that, within
the loop, Gui::Selection().addSelection() gets called and that ends up
calling App::Document::addObject() which pushes an object to the vector that
the loop is traversing.  If the vector is full, its storage is reallocated
and this means that later iterations of the loop are using invalid iterators.
Thus, one ends up with a bogus obj pointer and there will be a crash within
getGroupOfObject().  The problem was observed when using Arch Survey.

src/Gui/CommandView.cpp

@@ -2925,7 +2925,8 @@ static void doSelect(void* ud, SoEventCallback * cb)
             Gui::Selection().clearSelection(doc->getName());
         }
 
-        for(auto obj : doc->getObjects()) {
+        const std::vector<App::DocumentObject*> objects = doc->getObjects();
+        for(auto obj : objects) {
             if(App::GeoFeatureGroupExtension::getGroupOfObject(obj))
                 continue;