@CurrentTenant never affects app behavior

### Task List

- [x] Steps to reproduce provided
- [x] Stacktrace (if present) provided
- [x] Example that reproduces the problem uploaded to Github
- [x] Full description of the issue provided (see below)

### Steps to Reproduce

1. Setup MT app
2. Apply @WithoutTenant to a method in controller
3. Apply @CurrentTenant to a method in a service

### Expected Behaviour

Service method would execute with current tenant

### Actual Behaviour

Without Tenant behavior in service annotated with CurrentTenant

### Environment Information

- **Operating System**: OSX
- **GORM Version:** 6.1.10
- **Grails Version (if using Grails):** 3.3.6
- **JDK Version:** 8u161

### Example Application

https://github.com/erichelgeson/mttests/blob/master/grails-app/controllers/mttests/CurrentController.groovy#L35

There are other scenarios in this controller as well - I cant find a senario where `@CurrentTenant` would cause the results to differ than just not including the annotation.