FT: initialize mutexes
This function is reachable via cairo_ft_font_face_create_for_ft_face() -> _cairo_ft_unscaled_font_create_from_face() -> _cairo_ft_unscaled_font_create_internal() -> _cairo_ft_unscaled_font_map_lock(). Thus, it could happen that nothing initialized mutexes before this code runs.
Signed-off-by: Uli Schlachter psychon@znc.in