The blocklist cache is regenerated excessively

[jonasraoni]

The Blocklist.php has a _regenerateCache() method, which is called when a hash group (first 2 characters of the password hash) cannot be found.

Therefore if another user attempts to use the same non-catalogued hash group, the _regenerateCache() will be called again, and nothing will change.

The content of this cache is almost static, therefore it should be regenerated just on a first usage and when the user uploads/removes a blocklist.