wxMenu::GetTitle() returned a string in GTK+ format (i.e. using underscores
instead of ampersands) instead of the expected wx one.
This is, of course, the right thing to do and it also fixes
wxMenuBar::FindMenuItem() as a side effect.
Closes#12672.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66175 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775