Don't run unstuck if there is no simulation running in async case (#5799)
Don't run unstuck if there is no simulation running in async case.
In this case, the actor mPreviousPosition is not updated, so the actor position is interpolated between an old (stucked) position and the new (unstucked) position. The new position is most likely "stucked", so the unstuck code strikes again, making the actor "vibrates".
That's exactly what the sync code path does, and it doesn't exhibit this behavior.