CBQE-2517: update posinf fn

Change-Id: I76af67f4434777c58596d143aae1add0fe13bf4e
Reviewed-on: http://review.couchbase.org/44244
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>