by using std::assert rather thatn DBG_ASSERT.

Change-Id: I8fca2b82f8d86a843c024556a0a29c7848b1e602
Reviewed-on: https://gerrit.libreoffice.org/19294Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>