coerce_value(..) is a local static function without side effects

Change-Id: Id153ad26973b5724b33f144ae9eba49562b15067
Reviewed-on: https://gerrit.libreoffice.org/40040Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Jochen Nitschke <j.nitschke+logerrit@ok.de>