Fix inaccessible entities being incorrectly added to space view

[jleibs]

What

• Resolves: Broken space view added by heuristics #4221

Although is_reachable_by_transform correctly accounts for disconnected spaces, visit_descendants_with_reachable_transform was never modified to account for disconnected spaces correctly. The inconsistency leads to creating a space with unreachable content in it.

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