support the lack of a distinct_id on people...

.. by defaulting to other distinct_id

* fall back to events distinct_id when making decide request if
  there is no people profile distinct id

* do not merge experiment_id and variant_id into the $experiments
  property if there is no people profile
removed unnessisary error check

.. this should never happen
Merge branch 'master' into decide-query-wo-people
checkForVariantsOnActive is used