sdbox: Fixed race condition when one session opens a mailbox while another is still creating it. This happened mostly when nonexistent INBOX was being opened by multiple sessions at the same time.
sdbox: Fixed race condition when one session opens a mailbox while another is still creating it.
This happened mostly when nonexistent INBOX was being opened by multiple
sessions at the same time.

damoxc/dovecot,damoxc/dovecot,damoxc/dovecot,damoxc/dovecot,damoxc/dovecot