[Dovecot] mail_log plugin logs UTF-8 mailbox name

A small bug in the mail_log plugin:

When I copy a mail from the inbox to a mailbox with special characters, the mailbox name is logged in UTF-8:

[...] copy from INBOX: box=INBOX.Euro €, [...]

I guess the name should be in mUTF-7, like it is done when I copy the other way round:

[...] copy from Euro &IKw-: box=INBOX, [...]