corrected a too eager error message (patch 648599)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@18078 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/mdi.cpp

@@ -1352,7 +1352,12 @@ static void RemoveWindowMenu(wxWindow *win, WXHMENU menu)
         {
             if ( !::GetMenuString(hMenu, i, buf, WXSIZEOF(buf), MF_BYPOSITION) )
             {
-                wxLogLastError(wxT("GetMenuString"));
+                // Ignore successful read of menu string with length 0 which
+                // occurs, for example, for a maximized MDI childs system menu
+                if ( ::GetLastError() != 0 )
+                {
+                    wxLogLastError(wxT("GetMenuString"));
+                }
 
                 continue;
             }