tx21 Cancel action that affects no active tx21's - valid or invalid?

[marv-engine]

@m21 - what does the tx21 code currently do with any of the Cancel actions if there are no active tx21's that match? Is that considered an invalid tx or just that no tx21's were affected? The spec doesn't say what should happen in that case.

Also, for tx20, the spec doesn't say what should happen for an Update or Cancel action if there's no matching active sell offer. It is invalid to attempt to close a crowdsale that is not active. These are similar situations, so the code should handle tx20, tx21 and tx53 the same way unless there's a reason not to.

[m21]

Correct, it fails (is marked invalid) just like a send or trade from invalid property would, etc.
There is nothing else to do really :)
Anything that is not found or doesn't pass the various checks (ecosystem, ownership, etc.) - fails
It's a binary flag on every MP TX that MasterCore has: valid or invalid (though various internal error codes).
That binary flag + some TX info is stored for every MP TX as we parse (going forward).