Relater: rhbz#903281 NULL follow frames on drag/drop

Change-Id: I50319fb218518edd23ff8c859c355265595050d6
(cherry picked from commit f141505929c95c97ae4765d7c7221f07e41ef8e7)
Reviewed-on: https://gerrit.libreoffice.org/6926
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>