Since we use contextual messages, we need to concatenate:
- context
- EOT character
- the message itself
see https://www.gnu.org/software/gettext/manual/html_node/MO-Files.html

A priori, regression from 00657aef

Change-Id: Ie3e781e30ce09f0121afff2f0eb0769b1fbd2114
Reviewed-on: https://gerrit.libreoffice.org/47521Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Jean-Baptiste Faure <jbfaure@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>