Bug: The goal on the agent isn't cleared when a goal is completed

[crashkonijn]

Describe the bug
When a goal is completed, the goal isn't cleared before the OnGoalCompleted event is being called. If the same goal is being set on the agent again it stops processing (it's the same goal) and this is confusing.

Clearing this could end up in a loop (with a frame delay), but is much more clear in what's happening.

Steps to Reproduce
Steps to reproduce the behavior:

1. Wait for a goal to complete
2. In the OnGoalCompleted handler set the same goal again

Expected behavior
It would be better if the goal is cleared.