indexer-worker: Don't crash if we failed to get mailbox path. Found by Coverity
indexer-worker: Don't crash if we failed to get mailbox path.
Found by Coverity

LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot