PoolBase.sol: Consider returning 0 instead of reverting in LockToToken()

[code423n4]

Handle

hickuphh3

Vulnerability details

Impact

In the LockToToken() function, should either the stake balance or the lockToken total supply return 0, the function reverts with NO_DATA.

However, in the (hopefully) rare scenario where the entire stake balance is used for a payout, the function should return 0 instead of reverting.

Recommended Mitigation Steps

Consider returning 0 in the case where balance == 0. Perhaps a zero value can be returned in the case where totalLock is zero as well.