Also: Make destructor of SfxListener more robust, so that it can be used
in tests.

Change-Id: I02b273ca8e527705c2d3ea3295ed0dec1c4f83ae
Reviewed-on: https://gerrit.libreoffice.org/16483Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>