[Devel] FT_Get_BDF_Property neglects to check for NULL get_interface

[Keith Packard]

Some drivers (winfont in particular) don't set get_interface, causing:

    if ( face != NULL && face->driver != NULL )
    {
      FT_Driver              driver = face->driver;
      BDF_GetPropertyFunc    func;

      func = (BDF_GetPropertyFunc) driver->root.clazz->get_interface(
                             FT_MODULE( driver ), "get_bdf_property" );
      if ( func )
        error = func( face, prop_name, aproperty );
    }

to jump through a NULL pointer.

-keith