Determine reward distribution behavior when all accounts have zero earned rewards for epoch

[woodenfurniture]

We should determine what happens when all accounts have zero earned rewards for the epoch, and there is a non-zero amount to distribute:

• in the contract with forge test converage
• in the rewards distribution CLI with jest test coverage

[woodenfurniture]

Some basic validation is done in the CLI here https://github.com/shapeshift/rFOX/pull/64/files