Don't crash at mail_cache_lock() if mail_cache_map() fails.
Don't crash at mail_cache_lock() if mail_cache_map() fails.

--HG--
branch : HEAD

dscho/dovecot,jkerihuel/dovecot,jwm/dovecot-notmuch,jkerihuel/dovecot,jwm/dovecot-notmuch,jkerihuel/dovecot,jkerihuel/dovecot,dscho/dovecot,dscho/dovecot,dscho/dovecot,dscho/dovecot,jwm/dovecot-notmuch,jkerihuel/dovecot,jwm/dovecot-notmuch,jwm/dovecot-notmuch