Handling attachments when part parameters include filename or name

This is my first PR... I hope it's done right!

The problem: some attachments didn't have the ifdisposition=1 within the part structure, so the original code missed them.

The solution: I grab the part parameters and check if the 'name' or 'filename' properties exist, indicating a file attachment.

PhpStorm changed some formatting which shows up in the diff...