Test for x, y in GetPosition

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@34251 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/mdi.cpp

@@ -839,8 +839,10 @@ void wxMDIChildFrame::DoGetPosition(int *x, int *y) const
   wxMDIParentFrame *mdiParent = (wxMDIParentFrame *)GetParent();
   ::ScreenToClient((HWND) mdiParent->GetClientWindow()->GetHWND(), &point);
 
-  *x = point.x;
-  *y = point.y;
+  if (x)
+      *x = point.x;
+  if (y)
+      *y = point.y;
 }
 
 void wxMDIChildFrame::InternalSetMenuBar()