don't crash if we have no accelerators for the "Window" menu items

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@58493 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/mdi.cpp

@@ -732,7 +732,7 @@ bool wxMDIParentFrame::MSWTranslateMessage(WXMSG* msg)
     // but it doesn't check for the (custom) accelerators of the window menu
     // items as it's not part of the menu bar as it's handled by Windows itself
     // so we need to do this explicitly
-    if ( m_accelWindowMenu->Translate(this, msg) )
+    if ( m_accelWindowMenu && m_accelWindowMenu->Translate(this, msg) )
         return true;
 #endif // wxUSE_MENUS && wxUSE_ACCEL