Refactor FeeSplitter::getAmountDue to save one variable slot

[code423n4]

Handle

pmerkleplant

Vulnerability details

Impact

Function getAmountDue in FeeSplitter.sol defines the variable
totalReceived in line 83 eventhough it is already known if the variable is
even necessary.

The variable is uneccessary if _tokenRecords.totalShares == 0.
Not declaring it, if not necessary, saves gas.

Recommended Mitigation Steps

Rewrite the function to something like:

TokenRecords storage _tokenRecords = tokenRecords[address(_token)];
if (_tokenRecords.totalShares == 0) return 0;
uint256 totalReceived = _tokenRecords.totalReleased + _token.balanceOf(address(this));
// Rest same as before