[3.3.11] Controller redirect appends URL to existing URL

### Task List

- [X] Steps to reproduce provided
- [ ] 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. Download Grails v3.3.2
2. Clean, Compile, Run application
3. Verify running
4. Create a link with a "redirect action:''" directive
5. Click link
6. Verify if redirection happens
7. Stop application
8. Open gradle.properties
9. Change grailsVersion to 3.3.11
10. Repeat step 2 and 6

### Expected Behaviour

Redirection happens without a problem

### Actual Behaviour

- Returns a 404 error
- redirect appends a URL to existing URL

### Environment Information

- **Operating System**: Windows 10 20H2
- **Grails Version:** 3.3.11
- **JDK Version:** 1.8.0_281
- **Container Version (If Applicable):** None

### Example Application

- [Get it here](https://sourceforge.net/projects/ro3-pos/).

Start by reproducing the redirect problem in the linked example application, first with Grails 3.3.2 and then with 3.3.11 as described in the steps. Inspect the version change in gradle.properties and verify that the redirect no longer appends to the existing URL or returns a 404.

Written by the indexing model from the issue text.