Unnecessary currentEpoch zero check in StandardGovernor and ThresholdGovernor
Description
The currentEpoch value is derived from BatchGovernor._clock, which can never be zero. But the execute functions of both StandardGovernor and ThresholdGovernor check if currentEpoch is zero.
Recommendation
Since the epoch implementation being used doesn't allow for a zero value returned by _clock, consider removing these zero checks.
Status
Addressed in #1c7576f.