commit eca5ea9f
"make the AbstractDialog stuff extend from VclReferenceBase"
introduced this regression.

Fix up the asynchronous delete to work again - necessary because
the delete is triggered from deep inside the object it wants to
delete.

Change-Id: I18d5a899fbb2da772552ebba7fe6a8e810314010
Reviewed-on: https://gerrit.libreoffice.org/33881Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>