Fix issue where unwrapped errors are nil

[pkramer-irco]

When wrapping and unwrapping an error using the embedded ErrorWrapper type, the unwrapped error was nil which made it impossible to determine the error that was returned from the Keyfunc.

[lggomez]

Hi @pkramer-irco, per #462 this repo has been deprecated and migrated to a new organization: https://github.com/golang-jwt/jwt

As stated in golang-jwt/jwt#7, none if the new maintainers will be copying the original implementations of PRs of interest to respect the authors, but will rather encourage them to migrate to the new repo (and also check if their contribution is still applicable)

• The current default branch is main, respecting the old v3 version of this package: https://github.com/golang-jwt/jwt
• For changes that are break API-compatibility, the v4 branch is recommended (which will be later on merged to main): https://github.com/golang-jwt/jwt/tree/v4

Regards