Resolve "WebIDE doesn't work on empty repositories again"

What does this MR do?

For empty repositories, currentBranchId was '', it should default to the branchId picked up from the route URL. This MR fixes it.

Issue: #34522 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content