regression from
    commit 082e69fe
    Date:   Mon Feb 26 16:53:37 2018 +0000
    convert various MessBox to weld::MessageDialog

Change-Id: Ia9cef4de4ae9c13201c838f20f0ba6b6cff7f35d
Reviewed-on: https://gerrit.libreoffice.org/68490
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>