Allow claimEarnings when current round is not initialized

[yondonfu]

At the moment, BondingManager.claimEarnings() cannot be invoked when the current round is not initialized. This logic should be changed to the following:

require(_endRound < roundsManager().currentRound() || (_endRound == roundsManager().currentRound() && roundsManager().currentRoundInitialized()))

If the current round is initialized, a user should be able to claim earnings through the current round. If the current round is not initialized, a user should be able to claim earnings through current round - 1. The latter condition is because if the current round is not initialized and the user claims earnings through the current round and then the current round is subsequently initialized then it is possible for a delegator to have rewards and fees associated with the round that it will not be able to claim anymore because its lastClaimRound is already set to the current round at this point.