deth_ctf - Vault cannot be locked again by its owner

[ghost]

Description of the Bug:

A Vault contract has a public boolean locked which indicates whether the contract can accept ether or not. Using unlock will change its value to false allowing future transactions. However, if an owner of Vault wants to lock it once again, there is no functionality that allows it.

Impact:

There is no way owner lock its Vault contract again.

Solution:

Create a new event Locked(address owner) and a new function which can lock a Vault again

function lock() external onlyOwner {
        locked = true;
        emit Locked(msg.sender);
    }

[0xdeth]

This is design.