fix(authentication-oauth): Properly handle all oAuth errors

[daffl]

This pull request ensures that Grant oAuth errors are properly handled. Thanks to @tjenkinson for finding this.

• Closes https://github.com/feathersjs/feathers/issues/3275
• Closes https://github.com/feathersjs/feathers/issues/3266
• Closes https://github.com/feathersjs/feathers/pull/3267
• Closes https://github.com/feathersjs/feathers/issues/3276

[tjenkinson]

Thanks!