Fix unintended returning to pool with cancelImmediately

[hadashiA]

#553

Problem

It was a cancelImmediately issue.

1. When cancelImmediately is cancelled, the object is returned to the object pool immediately,
2. MoveNext in the Player Loop is still running even after it is returned to the pool.
3. if we enter MoveNext in the initialized state, it would probably stop immediately, But if it was canceled immediately and reused on the same frame as the pool, it would not stop, and the elapsed += Time.deltaSpan would be doubly elapsed....

Fix

If cancel Immediately, the return to the pool is abandoned.

NOTE:

• I thought about delaying the return until MoveNext, but there would be a problem if the return timing is different from the await timing.