It fix issue 577

It fix https://github.com/away3d/away3d-core-fp11/issues/577

If i want to know is material have any methods and try do it like this:
getMethodAt(0), i will catch error because of:
ShaderMethodSetup.getMethodAt { return
EffectMethodBase(_methods[index].method); }

It should check _methods length and return null if legnth is 0