show_head_ref(): check the result of resolve_ref_namespace()

Only use the result of resolve_ref_namespace() if it is non-NULL.

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

http-backend.c

@@ -484,9 +484,9 @@ static int show_head_ref(const char *refname, const struct object_id *oid,
 		const char *target = resolve_ref_unsafe(refname,
 							RESOLVE_REF_READING,
 							unused.hash, NULL);
-		const char *target_nons = strip_namespace(target);
 
-		strbuf_addf(buf, "ref: %s\n", target_nons);
+		if (target)
+			strbuf_addf(buf, "ref: %s\n", strip_namespace(target));
 	} else {
 		strbuf_addf(buf, "%s\n", oid_to_hex(oid));
 	}