parse_cmd_verify(): copy old_sha1 instead of evaluating <oldvalue> twice

Aside from avoiding a tiny bit of work, this makes it transparently
obvious that old_sha1 and new_sha1 are identical.  It is arguably a
bit silly to have to set new_sha1 in order to verify old_sha1, but
that is a problem for another day.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/update-ref.c

@@ -249,7 +249,7 @@ static const char *parse_cmd_verify(struct strbuf *input, const char *next)
 
 	if (!parse_next_arg(input, &next, &value)) {
 		update_store_old_sha1(update, value.buf);
-		update_store_new_sha1(update, value.buf);
+		hashcpy(update->new_sha1, update->old_sha1);
 	} else if (!line_termination)
 		die("verify %s missing [<oldvalue>] NUL", ref.buf);