fast-import: Fix crash when referencing already existing objects

Commit a5c1780a03 sets the pack_id of existing
objects to MAX_PACK_ID. When the same object is referenced later again it is
found in the local object hash. With such a pack_id fast-import should not try
to locate that object in the newly created pack(s).

Signed-off-by: Simon Hausmann <simon@lst.de>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

fast-import.c

@@ -1013,7 +1013,7 @@ static void load_tree(struct tree_entry *root)
 		return;
 
 	myoe = find_object(sha1);
-	if (myoe) {
+	if (myoe && myoe->pack_id != MAX_PACK_ID) {
 		if (myoe->type != OBJ_TREE)
 			die("Not a tree: %s", sha1_to_hex(sha1));
 		t->delta_depth = 0;