Remove unnecessary assert from wxMenuBar::MSWGetMenu().

This assert was triggered after the changes of the previous commit as we can
get WM_MENUSELECT with menu bar handle as parameter from Windows and still
search for the menu with this handle -- and there is nothing wrong with this,
so just return NULL but without asserting in this case.

This corrects the changes of r67355, see #13080.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78231 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/menu.cpp

@@ -1634,8 +1634,10 @@ void wxMenuBar::Detach()
 // get the menu with given handle (recursively)
 wxMenu* wxMenuBar::MSWGetMenu(WXHMENU hMenu)
 {
-    wxCHECK_MSG( GetHMenu() != hMenu, NULL,
-                 wxT("wxMenuBar::MSWGetMenu(): menu handle is wxMenuBar, not wxMenu") );
+    // If we're called with the handle of the menu bar itself, we can return
+    // immediately as it certainly can't be the handle of one of our menus.
+    if ( hMenu == GetHMenu() )
+        return NULL;
 
 #if wxUSE_OWNER_DRAWN
     // query all menus