Fix scene_viewer setup retry when mesh AABBs are missing

[fmterrors]

Objective

Ensure that scene_viewer initializes its controllable camera and default light even when loaded scene meshes do not have Aabb components on the first setup attempt.

When SceneHandle::is_loaded becomes true, mesh bounds may still be pending. The setup system currently marks its local setup state before checking for missing Aabb components. If any mesh is missing an Aabb, the system returns and permanently skips the camera and light initialization.

Solution

Set the local setup flag only after the scene bounds have been calculated and the camera and light initialization logic has completed.

This allows the system to retry on subsequent frames while any mesh is still waiting for its Aabb.

Testing

• cargo +nightly-2026-09-01 check --example scene_viewer --features free_camera,bevy_dev_tools
• rustfmt --edition 2024 --check examples/tools/scene_viewer/main.rs
• git diff --check

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