Fix event add/remove, Fix #149

[UlyssesWu]

This PR fixes #149 .

event Action iFix;

[IFix.Patch]
public void Test() {
	Action bug = () => Debug.Log("Full of bugs");
	iFix += bug;
}

Expect: Nothing was wrong.

Actual: ExecutionEngineException: Attempting to call method 'System.Threading.Interlocked::CompareExchange<...>' for which no ahead of time (AOT) code was generated.

Wrong explaination:

Correct explaination:

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