Test when invokefunction with wallet open, since the wallet not sign, witness is null.

then send the transaction, check applicationlog, this time witness is not null.

@csmuller please have a check.

@erikzhang Need your review.

I think we can just remove the syscall IsStandardContract. It is useless now.

@shargon Do we have any scenario to call IsStandardContract? Seems it's impossible to do this in contract.

@shargon Do we have any scenario to call IsStandardContract? Seems it's impossible to do this in contract.

No, @roman-khimov what do you think?

@shargon Do we have any scenario to call IsStandardContract? Seems it's impossible to do this in contract.

No, @roman-khimov what do you think?

#1753, option №4 wins.

Merge?

Please remove this syscall's price in document. Thanks.
https://docs.neo.org/docs/zh-cn/reference/fees.html.