Made reading/writing undo info a bit more robust.
diff --git a/src/fileio.c b/src/fileio.c
index f8375c6..101c804 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -2588,7 +2588,7 @@
 	char_u	hash[UNDO_HASH_SIZE];
 
 	sha256_finish(&sha_ctx, hash);
-	u_read_undo(NULL, hash);
+	u_read_undo(NULL, hash, fname);
     }
 #endif