this is similar to...

commit d17d9500
Date:   Tue Apr 16 14:49:46 2019 +0100

    tdf#124597 template select dialog launched before parent gets final size

where the dialog is launched before its parent window has got to its final size

Change-Id: I0f54a8da482ed75fa939e230b69c0eb918782bf5
Reviewed-on: https://gerrit.libreoffice.org/70943
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>