Fix URL handling.

[GoebelL]

Changes in this Pull Request:

• Corrected BIRT base URL injection in viewer.properties.

Mandatory checks:

• [X] latest changes were fetched from the upstream branch before creating this PR (branch is up to date)
• [ ] changes were tested manually
• [ ] communication about interdependent changes has been sent to the team (if applicable)
• [ ] respective Jenkins jobs were referenced in additional context section of this PR

OSCM Build References: Not yet

---

This change is