Fix No Token exception when tokenRequired is set to false

[SkyLeite]

This is a fix for the following issue: https://nuxtjs.cmty.io/nuxt/docs/issues/c84

[pi0]

Thanks for the PR. While I agree about the bug, it may be better we don't assume anything about scheme options handling in the core.

[SkyLeite]

I don't understand, can you elaborate?

[pi0]

@Kxze strategy.options and tokenRequired are things specific to the schemes but we validating options outside of scheme. (What if a scheme doesn't set options on itself?)

Maybe it would be better to merge it with L250 and totally remove Promise.reject line:

if (!_endpoint.headers['Authorization'] && isSet(token)) {
...
}

[pi0]

Thank you!