Fix java.util.Calendar.set in integration.forms.DateValidator

Change-Id: I1bd87c623b923469c325ebfcba4ba82e2a648ae2
Reviewed-on: https://gerrit.libreoffice.org/11694
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>