Fix Vue warning in Security inventory breadcrumbs during load

What does this MR do and why?

Removes a Vue [Vue warn]: Invalid prop: custom validator check failed for prop "items" warning that appears in the browser console every time a user opens the Security inventory page.

The warning came from RecursiveBreadcrumbs, which built a crumb from this.group.name before the Apollo GroupAvatarAndParentQuery resolved. During that brief loading window the crumb had text: undefined, which fails GlBreadcrumb's items validator (each item requires a truthy text). The crumbs computed now falls back to the accumulated items prop until group.name is populated, so no invalid item ever reaches GlBreadcrumb.

References

• issue: Vue warning: invalid items prop in Security inv... (#615433 - closed)

Screenshots or screen recordings

Before	After
Console warning on every load	No warning

How to set up and validate locally

1. Open a group in the local GDK and navigate to Secure > Security inventory.
2. Open the browser DevTools console before or during the initial load.
3. Verify no [Vue warn]: Invalid prop: custom validator check failed for prop "items" message appears.
4. Navigate into a subgroup via the sidebar; the breadcrumb path should render correctly and no warning should fire.
5. Run yarn jest ee/spec/frontend/security_inventory/components/recursive_breadcrumbs_spec.js and confirm all three tests pass, including the new "while the group query is still loading" case.

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