Only use ASCII characters for attachment file names and limit length
Since the ZIP format is rather annoying with file name encoding (it's undefined), all attachment file names should be ASCII.
For non-ASCII file names, strip any non-ASCII character and add a hash code to the filename, e.g. like:
"File with wéïrd châractërs.txt" => "File with wrd chractrs-9dc058.txt"
Also, limit total file path lengths to 255 characters