+ initialize pSalBmp+pSalMask to nullptr

Change-Id: I320e9cf98ef8224e98303bec1e58f59dc5b1ad4e
Reviewed-on: https://gerrit.libreoffice.org/41097Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>