just hit this with the same all-modal hammer we now use in the extension manager,
a modeless dialog, with modal subdialogs run by a normal non-async subloop, turns
into a modal dialog for all other toplevels

Change-Id: Ia35fad7a1be2ec493011c7e4354b70231b78a7fc
Reviewed-on: https://gerrit.libreoffice.org/65503
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>