packfile: stop using linked MIDX list in find_pack_entry()

Refactor `find_pack_entry()` so that we stop using the linked list of
multi-pack indices. Note that there is no need to explicitly prepare
alternates, and neither do we have to use `get_multi_pack_index()`,
because `prepare_packed_git()` already takes care of populating all data
structures for us.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

packfile.c

@@ -2074,16 +2074,15 @@ static int fill_pack_entry(const struct object_id *oid,
 int find_pack_entry(struct repository *r, const struct object_id *oid, struct pack_entry *e)
 {
 	struct list_head *pos;
-	struct multi_pack_index *m;
 
 	prepare_packed_git(r);
-	if (!r->objects->packed_git && !r->objects->multi_pack_index)
-		return 0;
 
-	for (m = r->objects->multi_pack_index; m; m = m->next) {
-		if (fill_midx_entry(r, oid, e, m))
+	for (struct odb_source *source = r->objects->sources; source; source = source->next)
+		if (source->midx && fill_midx_entry(r, oid, e, source->midx))
 			return 1;
-	}
+
+	if (!r->objects->packed_git)
+		return 0;
 
 	list_for_each(pos, &r->objects->packed_git_mru) {
 		struct packed_git *p = list_entry(pos, struct packed_git, mru);