When decreasing lockup, `modifyRailLockup` first performs `settleAccountLockup`

Suppose the operator attempts to `modifyRailLockup` to reduce the `lockupPeriod`. I think we only need to do `settleAccountLockup` after and not before.

The impact is that if a user has enough funds for the `lockupPeriod` after but not before the modification, the operation will revert.

I think the same problem also applies to `modifyRailPayment`.

I think that we only really need to `settleAccountLockup` after the operation.