make a zero address check on SecuredLine.rollover

[code423n4]

Lines of code

https://github.com/debtdao/Line-of-Credit/blob/audit/code4rena-2022-11-03/contracts/modules/credit/SecuredLine.sol#L48

Vulnerability details

Impact:
Making a zero address check on variable address newline will reduce a risk of making maliciously newline equal to zero address which can stop a function from being deployed on new line address.

Proof of concept:

https://github.com/debtdao/Line-of-Credit/blob/audit/code4rena-2022-11-03/contracts/modules/credit/SecuredLine.sol#L48

EscrowedLine._rollover(newLine);
https://github.com/debtdao/Line-of-Credit/blob/audit/code4rena-2022-11-03/contracts/modules/credit/SecuredLine.sol#L59

which can further effect _rollover function in EscrowedLine.sol contract.
function _rollover(address newLine) internal virtual returns(bool) {
require(escrow.updateLine(newLine));
return true;
}
https://github.com/debtdao/Line-of-Credit/blob/audit/code4rena-2022-11-03/contracts/modules/credit/EscrowedLine.sol#L89

Recommendation:
Make a necessary zero address check.

[dmvt]

Zero address checks are considered QA.

[c4-judge]

dmvt marked the issue as unsatisfactory:
Overinflated severity