because the call site specifies millis in a sal_uInt64 variable

Change-Id: I5cf42407b9e7f3cdef976d8f442609723fd67af9
Reviewed-on: https://gerrit.libreoffice.org/68342
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>