`TroveManager``_calcBorrowingRate` always returns `borrowingFeeFloor`

[GalloDaSballo]

Impact

_calcBorrowingRate is using min(X + Y, X) meaning it will always return X in this case borrowingFeeFloor

Mitigation

Change

  function _calcBorrowingRate(uint _stableCoinBaseRate) internal view returns (uint) {
    return LiquityMath._min(borrowingFeeFloor + _stableCoinBaseRate, borrowingFeeFloor);
  }

To

  function _calcBorrowingRate(uint _stableCoinBaseRate) internal view returns (uint) {
    return LiquityMath._min(borrowingFeeFloor + _stableCoinBaseRate, 1e18);
  }

[sambP]