reset rewardsLocked to 0 when no longer used

[code423n4]

Handle

gpersoon

Vulnerability details

Impact

The function _stake() initializes endEpoch using the value of rewardsLocked.
Afterwards rewardsLocked is no longer used (because now endEpoch !=0)

So you can set rewardsLocked to 0 save a bit of gas.

Proof of Concept

https://github.com/code-423n4/2021-10-covalent/blob/ded3aeb2476da553e8bb1fe43358b73334434737/contracts/DelegatedStaking.sol#L171-L176

Tools Used

Recommended Mitigation Steps

Update to code of _stake() to:
if (endEpoch == 0) {
endEpoch = uint128(block.number) + rewardsLocked / allocatedTokensPerEpoch;
rewardsLocked = 0; // no longer used and saves a bit of gas
}

[GalloDaSballo]

I believe gas refunds have bee removed when EIP-1559 made it to mainnet, that said, the sponsor has applied the improvement