Use wxFrame::FindItemInMenuBar() in ProcessCommand().

Don't duplicate FindItemInMenuBar() code in ProcessCommand() and, more
importantly, use the overridden version of FindItemInMenuBar() in MDI parent
frame in wxMSW to allow using ids corresponding to the active child frame menu
items.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71112 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/framecmn.cpp

@@ -242,11 +242,7 @@ wxPoint wxFrameBase::GetClientAreaOrigin() const
 
 bool wxFrameBase::ProcessCommand(int id)
 {
-    wxMenuBar *bar = GetMenuBar();
-    if ( !bar )
-        return false;
-
-    wxMenuItem *item = bar->FindItem(id);
+    wxMenuItem* const item = FindItemInMenuBar(id);
     if ( !item )
         return false;