Two SafeApprove calls when it could be just one

[code423n4]

Handle

a_delamo

Vulnerability details

Impact

In LifeGuard3Pool and BaseVaultAdaptor contracts, we are doing two approve calls when we could just use one. Doing two safeApprove calls with value = 0 and after value = max doesn't seem to provide any extra feature.

For example:

        IERC20(_token).safeApprove(address(_vault), 0);
        IERC20(_token).safeApprove(address(_vault), type(uint256).max);

[kitty-the-kat]

causes issues with usdt otherwise - could create separate logic to just deal with usdt, but is non-critical.