Not try to send messages from addresses with 0 balance.

[jennijuju]

A miner was trying to perform a lotus-miner actor withdraw with miner available balance being 3 FIL and worker address = 0 and got ERROR: GasEstimateMessageGas error: estimating gas used: message execution failed: exit SysErrSenderStateInvalid(2), reason: actor balance less than needed: 0 FIL < 0.00000101 FIL (RetCode=2)

We think the issue was b/c the first message is sent by worker address and in this case, gas cannot be paid with 0 FIL worker.

The error message is a little bit misleading here. Also, @arajasek suggested that we should improve our ux to not even try to send messages from addresses with 0 balance.

[arajasek]

Digging a little further, it looks like we already do have this check (the checkBalance method), it's just that the GasEstimateMessageGas check gets triggered and fails first. I think that's fine, a change isn't needed here.