refs: use skip_prefix() in ref_is_hidden()

This is shorter, makes the logic a bit easier to follow, and is
perhaps a bit faster too.

The logic is to make the final decision only when "subject" is there,
its early part matches "match", and the match is at the slash
boundary (or the whole thing).

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs.c

@@ -1066,7 +1066,7 @@ int ref_is_hidden(const char *refname, const char *refname_full)
 		const char *match = hide_refs->items[i].string;
 		const char *subject;
 		int neg = 0;
-		int len;
+		const char *p;
 
 		if (*match == '!') {
 			neg = 1;
@@ -1081,10 +1081,9 @@ int ref_is_hidden(const char *refname, const char *refname_full)
 		}
 
 		/* refname can be NULL when namespaces are used. */
-		if (!subject || !starts_with(subject, match))
-			continue;
-		len = strlen(match);
-		if (!subject[len] || subject[len] == '/')
+		if (subject &&
+		    skip_prefix(subject, match, &p) &&
+		    (!*p || *p == '/'))
 			return !neg;
 	}
 	return 0;