and fix bug where we were deleting a pointer to an object
we did not own via pFormatExchangeList

Change-Id: I488c679734c48bd21bc6be04837e037e97550647
Reviewed-on: https://gerrit.libreoffice.org/51668Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>