Nominator can stake less than minimum nominator stake

[vedhavyas]

A nominator can stake less than minimum nominator stake with following steps

• Nominator sends Withdraw all from an operator
• Sends another deposit less than minimum(order of this step will not matter, either before or after withdrawl but within same epoch)
  During epoch transition, since we process withdrawals first and then deposits after without checking minimum, then nominator will essentially, stake less than minimum.

This can be solved if we ensure there is only either Pending Deposit or Pending Withdrawal for a given epoch. They can send multiple Pending Deposits or Pending Withdrawals and amount gets accumulated until the epoch is finished.