so we can find where its been dragged from in order to remove it from that
source, rather than relying that it comes from the previously focused listbox

Change-Id: Ie6aa1a311b46e5e9ee96cab05e0705b794b5eb0b
Reviewed-on: https://gerrit.libreoffice.org/33575Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>