Fix error "ERROR in finalizer: wrong number of arguments for function…

… call" on closing

Luajit started printing these errors in their commit 1c27912 instead of
throwing them. The char **err argument is needed because all of the
impl's functions are wrapped with ffi_util.err_arg_to_multiple_return in
lfs.moon.

libaegisub/lua/modules/lfs.cpp

@@ -84,11 +84,11 @@ char *dir_next(DirectoryIterator &it, char **err) {
 	});
 }
 
-void dir_close(DirectoryIterator &it) {
+void dir_close(DirectoryIterator &it, char **err) {
 	it = DirectoryIterator();
 }
 
-void dir_free(DirectoryIterator *it) {
+void dir_free(DirectoryIterator *it, char **err) {
 	delete it;
 }