Don't leak the previous cache

Conflicts:
	dbaccess/source/core/api/RowSet.cxx

Change-Id: I61cb1c608a7de8efc63533085e86c6c17c05f545
Reviewed-on: https://gerrit.libreoffice.org/10795
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>