Custom activity type always marked "Failed"

Copied from #3215553: Custom activity type always marked "Failed", which has the exact same issue.

Given:
- a custom activity type without an "answer" component
- a non-mandatory module
- max score of zero

Expected:
- The result will be "passed", if the activity was completed, or "pending" if it was not

Observed:
- The result is always displayed "failed" because it has neither evaluation method nor answer type