[ISSUE #974] ArrayIndexOutOfBoundsException may be thrown when invokes taskDispatcher.addTask

[jifengnan]

What is the purpose of the change

Fixes #974 .

Brief changelog

加了一个新的通用的方法，解决Math.abs(Integer.MIN_VALUE)返回值为负数的问题。
Added a new util method to solve the issue that the return value of Math.abs may be negative.

Verifying this change

A unit test is added on TaskDispatcherTest.testAddTask, it works well now if the hashcode is Integer.MIN_VALUE

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[nkorange]

Thanks for your contribution. Next time point to alibaba:develop please :)

[jifengnan]

@nkorange Got it, thanks.