Once an order has been filled, no one should be able to cancel the order or mark the order as Cancelled.
The following code shows that the order maker can change the status of the order to Cancelled at any point of time.
https://github.com/code-423n4/2022-06-putty/blob/3b6b844bc39e897bd0bbb69897f2deff12dc3893/contracts/src/PuttyV2.sol#L526
Although changing the status of an order to Cancelled after it has been filled does not cause any lost of funds at the later stages (e.g. when exercising or withdrawing), it might cause unnecessary confusion to the users as it does not accurately reflect the status of an order on-chain.
Users might fetch the status of an order directly from the cancelledOrders mapping or poll the on-chain for emitted event, and come to a wrong conclusion that since the order has been cancelled, it has not been filled.
It is recommended to update the cancel function to only allow order maker to call this function only if an order has not been filled.
