refs: pass NULL to refs_resolve_ref_unsafe() if hash is not needed

This allows us to get rid of two write-only variables, one of them
being a SHA1 buffer.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs/files-backend.c

@@ -1676,13 +1676,12 @@ static int commit_ref_update(struct files_ref_store *refs,
 		 * check with HEAD only which should cover 99% of all usage
 		 * scenarios (even 100% of the default ones).
 		 */
-		struct object_id head_oid;
 		int head_flag;
 		const char *head_ref;
 
 		head_ref = refs_resolve_ref_unsafe(&refs->base, "HEAD",
 						   RESOLVE_REF_READING,
-						   head_oid.hash, &head_flag);
+						   NULL, &head_flag);
 		if (head_ref && (head_flag & REF_ISSYMREF) &&
 		    !strcmp(head_ref, lock->ref_name)) {
 			struct strbuf log_err = STRBUF_INIT;

worktree.c

@@ -307,7 +307,6 @@ const struct worktree *find_shared_symref(const char *symref,
 	for (i = 0; worktrees[i]; i++) {
 		struct worktree *wt = worktrees[i];
 		const char *symref_target;
-		unsigned char sha1[20];
 		struct ref_store *refs;
 		int flags;
 
@@ -327,7 +326,7 @@ const struct worktree *find_shared_symref(const char *symref,
 
 		refs = get_worktree_ref_store(wt);
 		symref_target = refs_resolve_ref_unsafe(refs, symref, 0,
-							sha1, &flags);
+							NULL, &flags);
 		if ((flags & REF_ISSYMREF) && !strcmp(symref_target, target)) {
 			existing = wt;
 			break;