fixing iterator use

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67213 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/osx/carbon/app.cpp

@@ -336,7 +336,7 @@ void wxApp::MacReopenApp()
     // if some windows are not hidden -> do nothing
 
     wxWindowList::compatibility_iterator node = wxTopLevelWindows.GetFirst();
-    if ( node == NULL )
+    if ( !node )
     {
         MacNewFile() ;
     }