Merge branch 'jk/virtual-objects-do-exist'

A recent update broke "is this object available to us?" check for
well-known objects like an empty tree (which should yield "yes",
even when there is no on-disk object for an empty tree), which has
been corrected.

* jk/virtual-objects-do-exist:
  rev-list: allow cached objects in existence check

builtin/rev-list.c

@@ -238,7 +238,7 @@ static inline void finish_object__ma(struct object *obj)
 static int finish_object(struct object *obj, const char *name, void *cb_data)
 {
 	struct rev_list_info *info = cb_data;
-	if (!has_object_file(&obj->oid)) {
+	if (oid_object_info_extended(the_repository, &obj->oid, NULL, 0) < 0) {
 		finish_object__ma(obj);
 		return 1;
 	}