Reintroduce !currentCluster for logo render condition

[rak-phillip]

Summary

This reintroduces that original !currentCluster condition for displaying the Rancher logo.

Fixes #15673

Occurred changes and/or fixed issues

• Reintroduce !currentCluster for logo render condition

Technical notes summary

The original PR replaced !currentCluster with a route test because currentCluster can be set to undefined. Introducing the condition for current cluster will allow for maintaining current behavior, with the added benefit of eliminating the "flashing" behavior with the route check.

Areas or cases that should be tested

Navigating between routes in dashboard.

Imported Harvester clusters.

Areas which could experience regressions

Same as to test - the logo needs to render consistently.

Screenshot/Video

Checklist

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