[HarfBuzz] infinite loops in hb_ot_tag_from_language()

[Jonathan Kew]

Hi Behdad,

There are a couple of infinite loops (they fail to increment the counter variable) in hb_ot_tag_from_language(), in the "x-hbot..." case:

    while (i < 4 && IS_LETTER (lang_str[i])) {
      tag[i] = TO_UPPER (lang_str[i]);
    }
    while (i < 4)
      tag[i] = ' ';

Neither of these loops will ever terminate!

See https://bugzilla.mozilla.org/show_bug.cgi?id=603352. (Reported by timeless.)

JK