cifs: alloc_path_with_tree_prefix: do not append sep. if the path is empty

alloc_path_with_tree_prefix() concatenates tree prefix and the path.
Windows CIFS client does not add separator after the tree prefix if the path
is empty. Let's do the same.

This fixes mounting DFS namespaces with names containing non-ASCII symbols.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=215440Signed-off-by: Eugene Korenevsky <ekorenevsky@astralinux.ru>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2pdu.c

@@ -2587,8 +2587,13 @@ alloc_path_with_tree_prefix(__le16 **out_path, int *out_size, int *out_len,
 
 	cp = load_nls_default();
 	cifs_strtoUTF16(*out_path, treename, treename_len, cp);
-	UniStrcat(*out_path, sep);
-	UniStrcat(*out_path, path);
+
+	/* Do not append the separator if the path is empty */
+	if (path[0] != cpu_to_le16(0x0000)) {
+		UniStrcat(*out_path, sep);
+		UniStrcat(*out_path, path);
+	}
+
 	unload_nls(cp);
 
 	return 0;