The ecrecover() function returns an address of zero when the signature does not match. This can cause problems if address zero is ever the owner of assets, and someone uses the permit function on address zero. If that happens, any invalid signature will pass the checks, and the assets will be stealable. In this case, the asset of concern is the vaults ERC20 token, and fortunately OpenZeppelins implementation does a good job of making sure that address zero is never able to have a positive balance. If this contract ever changes to another ERC20 implementation that is laxer in its checks in favor of saving gas, this code may become a problem.
There is 1 instance of this issue:
https://github.com/code-423n4/2022-06-nibbl/blob/8c3dbd6adf350f35c58b31723d42117765644110/contracts/NibblVault.sol#L563
