[HarfBuzz] hb_font_funcs_is_immutable() is wrong

[Jonathan Kew]

Hi Behdad,

This function, from hb-font.cc, doesn't look right to me.....

  hb_bool_t
  hb_font_funcs_is_immutable (hb_font_funcs_t *ffuncs)
  {
    return ffuncs->immutable = TRUE;
  }

I suggest removing the "= TRUE" here!

(Maybe it'd be worth declaring the parameter as const for "query" functions like this -- then the compiler would have noticed this one.)

JK