Variable `loop` was uninitialized and resulted in an error when being
concatenated. Initialize the variable to blank: `local loop = ""`.

Close #6882
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
(cherry picked from commit a75ff33f2b426ffe02994b65a84cf70f178b1aee)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>