Don't activate hidden buttons when Enter is pressed in wxMSW.

The keyboard handling code could decide to activate a button which wasn't
currently visible at all, e.g. because it was on a non-current, and hence
hidden, page of a wxBookCtrl. This didn't make any sense, so check for the
button visibility before activating it.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76990 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/window.cpp

@@ -2536,7 +2536,7 @@ bool wxWindowMSW::MSWProcessMessage(WXMSG* pMsg)
                             }
                         }
 
-                        if ( btn && btn->IsEnabled() )
+                        if ( btn && btn->IsEnabled() && btn->IsShownOnScreen() )
                         {
                             btn->MSWCommand(BN_CLICKED, 0 /* unused */);
                             return true;