Fix too short picking ray in pinhole-only scenarios (rerun-io#7899)

### What
Details in the code comment.
I tried at first fixing the lack of contribution to the bounding box but
then realized that this is a can of worms.


![image](https://github.com/user-attachments/assets/83c03582-5641-45f5-aa40-78abfe7cfcbf)

### Checklist
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Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested the web demo (if applicable):
* Using examples from latest `main` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/7899?manifest_url=https://app.rerun.io/version/main/examples_manifest.json)
* Using full set of examples from `nightly` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/7899?manifest_url=https://app.rerun.io/version/nightly/examples_manifest.json)
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checklist](https://github.com/rerun-io/rerun/blob/main/tests/python/release_checklist)!
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`CHANGELOG.md` and the migration guide

- [PR Build Summary](https://build.rerun.io/pr/7899)
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crates/viewer/re_space_view_spatial/src/ui_3d.rs

@@ -888,8 +888,14 @@ fn add_picking_ray(
     let mut line_batch = line_builder.batch("picking ray");
 
     let origin = ray.point_along(0.0);
+
     // No harm in making this ray _very_ long. (Infinite messes with things though!)
-    let fallback_ray_end = ray.point_along(scene_bbox.size().length() * 10.0);
+    //
+    // There are some degenerated cases where just taking the scene bounding box isn't enough:
+    // For instance, we don't add pinholes & depth images to the bounding box since
+    // the default size of a pinhole visualization itself is determined by the bounding box.
+    let fallback_ray_end =
+        ray.point_along((scene_bbox.size().length() * 10.0).at_least(thick_ray_length * 10.0));
     let main_ray_end = ray.point_along(thick_ray_length);
 
     line_batch