Prevent crash due to malformed heirarchy (#254)

* Removed unwrap from `update_render_target_size` to prevent crash on startup

* Removed unnecessary import

Author: Freyja-moth

bevy_editor_panes/bevy_3d_viewport/src/lib.rs

@@ -118,10 +118,12 @@ fn render_target_picking_passthrough(
             continue;
         }
         for (pane_root, _viewport) in &viewports {
-            let content_node_id = children_query
+            let Some(content_node_id) = children_query
                 .iter_descendants(pane_root)
                 .find(|e| content.contains(*e))
-                .unwrap();
+            else {
+                continue;
+            };
 
             let image_id = children_query.get(content_node_id).unwrap()[0];
             let Ok((computed_node, global_transform, ui_image)) = node_query.get(image_id) else {