GetClock() needs it to properly scale and round the floating point
value. It also handles negative values, fiddling with that is only
needed for the [] formats.

Regression from

    commit e2e47898
    CommitDate: Fri Aug 31 12:50:52 2018 +0200

        Use tools::Time::GetClock() in number formatter for wall clock time

Change-Id: I05fe9e22886d4e59f110c0a826dadb43234d348a
Reviewed-on: https://gerrit.libreoffice.org/68508Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Jenkins