keep-core - stake operator should not be eligible if undelegatedAt is set
An operator's stake should not be eligible if they stake an amount and immediately call `undelegate` in an attempt to indicate that they are going to recover their stake soon.\\n```\\nbool notUndelegated = block.number <= operator.undelegatedAt || operator.undelegatedAt == 0;\\n\\nif (isAuthorized && isActive && notUndelegated) {\\n    balance = operator.amount;\\n}\\n```\\n
A stake that is entering undelegation is indicated by `operator.undelegatedAt` being non-zero. Change the `notUndelegated` check block.number <= `operator.undelegatedAt` || `operator.undelegatedAt` == 0 to `operator.undelegatedAT == 0` as any value being set indicates that undelegation is in progress.\\nEnforce that within the initialization period stake is canceled instead of being undelegated.
```\\nbool notUndelegated = block.number <= operator.undelegatedAt || operator.undelegatedAt == 0;\\n\\nif (isAuthorized && isActive && notUndelegated) {\\n    balance = operator.amount;\\n}\\n```\\n