demos: Use getc() if HAVE_GETC_UNLOCKED is not defined
demos: Use getc() if HAVE_GETC_UNLOCKED is not defined

demos/gtk-demo/demowindow.cc: Calls to getc() were removed by mistake by commit
6ed01325449fec47457bee741f9c7ec04887c04e. Reinsert them. Bug #748657.

johne53/MB3Gtkmm,GNOME/gtkmm,GNOME/gtkmm,GNOME/gtkmm,johne53/MB3Gtkmm,GNOME/gtkmm,johne53/MB3Gtkmm