fdo#51819: autorecovery: fix saving password in protected documents.

Thanks to sayt@mailinator.com for the idea.

Change-Id: Ib79abafe3d4d3ba21f7914aeb284d86ce662824c
(cherry picked from commit ef87ff6680f79362a431db6e7ef2f40cfc576219)
Reviewed-on: https://gerrit.libreoffice.org/8676
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Reviewed-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>