archive: simplify refname handling

There is no need to build a copy of the relevant part of the string just
to make sure we have a NUL-terminated string.  We can simply pass the
length of the interesting part to dwim_ref() instead.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

archive.c

@@ -260,18 +260,11 @@ static void parse_treeish_arg(const char **argv,
 	/* Remotes are only allowed to fetch actual refs */
 	if (remote) {
 		char *ref = NULL;
-		const char *refname, *colon = NULL;
-
-		colon = strchr(name, ':');
-		if (colon)
-			refname = xstrndup(name, colon - name);
-		else
-			refname = name;
-
-		if (!dwim_ref(refname, strlen(refname), sha1, &ref))
-			die("no such ref: %s", refname);
-		if (refname != name)
-			free((void *)refname);
+		const char *colon = strchr(name, ':');
+		int refnamelen = colon ? colon - name : strlen(name);
+
+		if (!dwim_ref(name, refnamelen, sha1, &ref))
+			die("no such ref: %.*s", refnamelen, name);
 		free(ref);
 	}