utf8: use correct type for values in interval table

We treat these as unsigned everywhere and compare against unsigned
values, so declare them using the typedef we already have for this.

While we're here, fix the indentation as well.

Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

utf8.c

@@ -5,8 +5,8 @@
 /* This code is originally from http://www.cl.cam.ac.uk/~mgk25/ucs/ */
 
 struct interval {
-  int first;
-  int last;
+	ucs_char_t first;
+	ucs_char_t last;
 };
 
 size_t display_mode_esc_sequence_len(const char *s)