The empty policy is crashed during flow.fail

[mishindm]

When a policy has empty 'properties:' or 'required:' attributes defined, but the 'throw:' property is populated in policy.yaml, the attempt to call flow.fail ends with crash in flow-engine on:

// 1. check the policy's own handler
if (currTask[type].catch) {

as currTask is null.

Adding some property is fixing the problem.