Check if 'Debugger.setAsyncCallStackDepth' method unimplemented

[itoys]

Fix for #226

[msftclas]

@itoys,
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[roblourens]

This won't fix it, the problem is that the runtime doesn't implement it. You need to call the method and ignore the error if it returns failure.

[itoys]

I already fixed it in my code. Just ignore that error. But I thought it's correct to check if method implemented.

[roblourens]

That check doesn't tell you if it's implemented, that object is just a proxy calling the target with whatever you give it.

[itoys]

Oh, I see. It won't work(