fix append and join of param parts

[oberix]

Hi, I think the indentation was messed up in decode_param. It make sense to me that value is appended to value_results at the and of the innermost for loop, and the value_results are joined outside the outermost loop, just before returning.

This was made clear with an email with an attachment whose filename contained a newline "\n", where only the part before the newline was actually present in the resulting filename.

Thanks
Regards