fc-lang: gracefully handle the case where the last language initial is < 'z'

FcLangSetIndex() contains code like this:

  low = fcLangCharSetRanges[firstChar - 'a'].begin;
  high = fcLangCharSetRanges[firstChar - 'a'].end;
  /* no matches */
  if (low > high)

The assumption behind this test didn't hold before this commit, unless
there is at least one language name that starts with 'z' (which is
thankfully the case in our world :-). If the last language name in
lexicographic order starts for instance with 'x', this change ensures
that fcLangCharSetRanges['y' - 'a'].begin and
     fcLangCharSetRanges['z' - 'a'].begin
are equal to NUM_LANG_CHAR_SET, in order to make the above assumption
correct in all cases.

fc-lang/fc-lang.c

@@ -561,6 +561,9 @@ main (int argc FC_UNUSED, char **argv)
 	while (setRangeChar <= c && c <= 'z')
 	    setRangeStart[setRangeChar++ - 'a'] = i;
     }
+    while (setRangeChar <= 'z') /* no language code starts with these letters */
+	setRangeStart[setRangeChar++ - 'a'] = i;
+
     for (setRangeChar = 'a'; setRangeChar < 'z'; setRangeChar++)
 	setRangeEnd[setRangeChar - 'a'] = setRangeStart[setRangeChar+1-'a'] - 1;
     setRangeEnd[setRangeChar - 'a'] = i - 1;