Do not show the remove button when the origin is empty (#5840)

### What

- Closes #5835

<img width="291" alt="image"
src="https://github.com/rerun-io/rerun/assets/49431240/6a7a204a-53d8-48ec-8e31-3f08619380ea">


### Checklist
* [x] I have read and agree to [Contributor
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 newly built examples:
[rerun.io/viewer](https://rerun.io/viewer/pr/5840)
* Using examples from latest `main` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/5840?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/5840?manifest_url=https://app.rerun.io/version/nightly/examples_manifest.json)
* [x] The PR title and labels are set such as to maximize their
usefulness for the next release's CHANGELOG
* [x] If applicable, add a new check to the [release
checklist](https://github.com/rerun-io/rerun/blob/main/tests/python/release_checklist)!

- [PR Build Summary](https://build.rerun.io/pr/5840)
- [Recent benchmark results](https://build.rerun.io/graphs/crates.html)
- [Wasm size tracking](https://build.rerun.io/graphs/sizes.html)

Author: abey79

crates/re_viewport/src/viewport_blueprint_ui.rs

@@ -573,53 +573,48 @@ impl Viewport<'_, '_> {
 
         let subdued = !space_view_visible || !visible;
 
-        let list_item = ListItem::new(ctx.re_ui, item_label)
+        let mut list_item = ListItem::new(ctx.re_ui, item_label)
             .selected(is_selected)
             .with_icon(guess_instance_path_icon(
                 ctx,
                 &InstancePath::from(entity_path.clone()),
             ))
             .subdued(subdued)
-            .force_hovered(is_item_hovered)
-            .with_buttons(|re_ui: &_, ui: &mut egui::Ui| {
-                let vis_response = if !empty_origin {
-                    let mut visible_after = visible;
-                    let vis_response =
-                        visibility_button_ui(re_ui, ui, space_view_visible, &mut visible_after);
-                    if visible_after != visible {
-                        if let Some(data_result_node) = data_result_node {
-                            data_result_node
-                                .data_result
-                                .save_recursive_override_or_clear_if_redundant(
-                                    ctx,
-                                    &query_result.tree,
-                                    &Visible(visible_after),
-                                );
-                        }
+            .force_hovered(is_item_hovered);
+
+        // We force the origin to be displayed, even if it's fully empty, in which case it can be
+        // neither shown/hidden nor removed.
+        if !empty_origin {
+            list_item = list_item.with_buttons(|re_ui: &_, ui: &mut egui::Ui| {
+                let mut visible_after = visible;
+                let vis_response =
+                    visibility_button_ui(re_ui, ui, space_view_visible, &mut visible_after);
+                if visible_after != visible {
+                    if let Some(data_result_node) = data_result_node {
+                        data_result_node
+                            .data_result
+                            .save_recursive_override_or_clear_if_redundant(
+                                ctx,
+                                &query_result.tree,
+                                &Visible(visible_after),
+                            );
                     }
+                }
 
-                    Some(vis_response)
-                } else {
-                    None
-                };
-
-                let mut response = remove_button_ui(
+                let response = remove_button_ui(
                     re_ui,
                     ui,
-                    "Remove group and all its children from the space view",
+                    "Remove this entity and all its children from the space view",
                 );
                 if response.clicked() {
                     space_view
                         .contents
                         .remove_subtree_and_matching_rules(ctx, entity_path.clone());
                 }
 
-                if let Some(vis_response) = vis_response {
-                    response |= vis_response;
-                }
-
-                response
+                response | vis_response
             });
+        }
 
         // If there's any children on the data result nodes, show them, otherwise we're good with this list item as is.
         let has_children = data_result_node.map_or(false, |n| !n.children.is_empty());