Disconnect "hide" menu signal to fix menu destruction in wxGTK.

The "hide" signal handler was triggered when destroying a sub-menu (even if it
was not shown at this time). Disconnect it to avoid asserts due to attempts to
generate an event for an already detached menu and to avoid the (bogus)
wxEVT_MENU_CLOSE event as well.

Closes #12668.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66082 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/menu.cpp

@@ -719,6 +719,11 @@ void wxMenu::Init()
 
 wxMenu::~wxMenu()
 {
+    // Destroying a menu generates a "hide" signal even if it's not shown
+    // currently, so disconnect it to avoid dummy wxEVT_MENU_CLOSE events
+    // generation.
+    g_signal_handlers_disconnect_by_func(m_menu, (gpointer)menu_hide, this);
+
     // see wxMenu::Init
     g_object_unref(m_menu);