read-cache: new API write_locked_index instead of write_index/write_cache

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache-tree.c

@@ -595,8 +595,7 @@ int write_cache_as_tree(unsigned char *sha1, int flags, const char *prefix)
 				      active_nr, flags) < 0)
 			return WRITE_TREE_UNMERGED_INDEX;
 		if (0 <= newfd) {
-			if (!write_cache(newfd, active_cache, active_nr) &&
-			    !commit_lock_file(lock_file))
+			if (!write_locked_index(&the_index, lock_file, COMMIT_LOCK))
 				newfd = -1;
 		}
 		/* Not being able to write is fine -- we are only interested