branch -d: simplify by using RESOLVE_REF_READING

When "git branch -d" reads the branch it is about to delete, it used
to avoid passing the RESOLVE_REF_READING ('treat missing ref as
error') flag because a symref pointing to a nonexistent ref would show
up as missing instead of as something that could be deleted.  To check
if a ref is actually missing, we then check

 - is it a symref?
 - if not, did it resolve to null_sha1?

Now we pass RESOLVE_REF_NO_RECURSE and the correct information is
returned for a symref even when it points to a missing ref.  Simplify
by relying on RESOLVE_REF_READING.

No functional change intended.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/branch.c

@@ -236,10 +236,11 @@ static int delete_branches(int argc, const char **argv, int force, int kinds,
 		free(name);
 
 		name = mkpathdup(fmt, bname.buf);
-		target = resolve_ref_unsafe(name, RESOLVE_REF_NO_RECURSE,
+		target = resolve_ref_unsafe(name,
+					    RESOLVE_REF_READING
+					    | RESOLVE_REF_NO_RECURSE,
 					    sha1, &flags);
-		if (!target ||
-		    (!(flags & REF_ISSYMREF) && is_null_sha1(sha1))) {
+		if (!target) {
 			error(remote_branch
 			      ? _("remote branch '%s' not found.")
 			      : _("branch '%s' not found."), bname.buf);