Rewards Can Become Permanently Unclaimable Due to Epoch Logic

[Skyge]

Description:
A logic flaw in the epoch and locking mechanism can cause deposited rewards to be permanently locked and unclaimable in two scenarios:

1. Initial Epoch Issue: Rewards deposited via depositReward() during epoch 0 are stored in epochReward[0]. However, the lock() function always begins locking from currentEpoch() + 1 (epoch 1). Consequently, rewards for epoch 0 have no corresponding lock positions and are irretrievable.

2. Empty Previous Epoch Issue: For any epoch n, if there are zero active lockers from the previous epoch (n-1), then rewards deposited for epoch n will also be unclaimable, as there is no eligible stake to distribute them to.

Recommendation:

• Prevent depositReward() from being called in epoch 0.
• Add a validation check to ensure there is existing eligible stake (lockers from epoch n-1) before accepting rewards for epoch n.