Bugfix for bullets randomly disappearing prematurely

[antfarmar]

This was how it was fixed in the earlier design.

• Invoke continues to execute even in a disabled script. It needs to be cancelled.
• The pool is a LIFO stack implementation
• The pool ends up using bullets whose Invoke has yet to execute (if it hit an asteroid and was pooled early, before the bullet's lifetime expiry)
• Hence, they were pooled again prematurely due to the outstanding Invoke.