Assume stake is elevated if currentRequiredStake reverts

[PlasmaPower]

As the currentRequiredStake docstring states:

    /**
     * @notice Calculate the current amount of funds required to place a new stake in the rollup
     * @dev If the stake requirement get's too high, this function may start reverting due to overflow, but
     * that only blocks operations that should be blocked anyway
     * @return The current minimum stake requirement
     */
    function currentRequiredStake(

We should assume the stake is elevated if this function reverts. I also swapped the order of the baseStake and currentRequiredStake checks, so that if all calls to the rollup are reverting for whatever reason, we'll correctly return an error there.

[joshuacolvin0]

LGTM