CP-5845: Fix partially applied helper function

The call_api_functions was only partially applied and so the function couldn't
be used as a comparitor for the Schwarzian transform sort.

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Merge pull request #1441 from simonjbeaumont/cp-5845-impl

CP-5845: Fix partially applied helper function