convert has_sha1_file() callers to has_object_file()

The only remaining callers of has_sha1_file() actually have an object_id
already. They can use the "object" variant, rather than dereferencing
the hash themselves.

The code changes here were completely generated by the included
coccinelle patch.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs.c

@@ -188,7 +188,7 @@ int ref_resolves_to_object(const char *refname,
 {
 	if (flags & REF_ISBROKEN)
 		return 0;
-	if (!has_sha1_file(oid->hash)) {
+	if (!has_object_file(oid)) {
 		error(_("%s does not point to a valid object!"), refname);
 		return 0;
 	}