[Dovecot] unwanted maildir directory

[Mike Abbott]

> imaptest logout=1 clients=4
> imaptest logout=1 user=tss2 box=shared/tss/INBOX clients=4

Yes, I can reproduce this assertion failure:
Panic: file maildir-save.c: line 79 (maildir_file_move): assertion failed: (*mf->tmp_name != '\0')
with:
imaptest clients=60 user=user\%d pass=test no_tracking logout=25 search=100 copybox=Copies

All of the crash backtraces have cmd_copy in common....
I'll try to narrow it down further (nix the search, turn off quotas, etc.).