don't use annoying and unneeded in C++ casts of NULL to "T *" in all other files neither

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@58227 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/mdi.cpp

@@ -1136,7 +1136,7 @@ bool wxMDIChildFrame::HandleMDIActivate(long WXUNUSED(activate),
     wxActivateEvent event(wxEVT_ACTIVATE, activated, m_windowId);
     event.SetEventObject( this );
 
-    ResetWindowStyle((void *)NULL);
+    ResetWindowStyle(NULL);
 
     return HandleWindowEvent(event);
 }