link_temp_to_file: don't leave the path truncated on adjust_shared_perm failure

Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/sha1_file.c b/sha1_file.c
index 47e2a29..5fcad28 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1383,8 +1383,10 @@
 	if (dir) {
 		*dir = 0;
 		mkdir(filename, 0777);
-		if (adjust_shared_perm(filename))
+		if (adjust_shared_perm(filename)) {
+			*dir = '/';
 			return -2;
+		}
 		*dir = '/';
 		if (!link(tmpfile, filename))
 			return 0;