Creating new label from group issue board fails

Summary

When trying to create a new label from the group issue board it fails. It works from the project issue board.

Steps to reproduce

1. Go to group issue board
2. Click on an issue
3. Click edit labels -> Create new label in the Sidebar
4. Submit a new label

What is the current bug behavior?

The request fails with 404 (path is not correct - it tries to access POST groups/undefined/labels )

What is the expected correct behavior?

A new label is created

In particular, a group label should be created.

/cc @victorwu