no modal for empty tree-group deletion (#4506)

* dont prompt for user confirmation for empty tree-group

* prettify code

CHANGELOG.md

@@ -17,6 +17,7 @@ For upgrade instructions, please check the [migration guide](MIGRATIONS.md).
  ### Changed
 - Reported datasets can now overwrite existing ones that are reported as missing, this ignores the isScratch precedence. [#4465](https://github.com/scalableminds/webknossos/pull/4465)
 - Users can now input floating point numbers into the rotation field in flight and oblique mode. These values will get rounded internally. [#4507](https://github.com/scalableminds/webknossos/pull/4507)
+- Deleting an empty tree group in the `Trees` tab no longer prompts for user confirmation. [#4506](https://github.com/scalableminds/webknossos/pull/4506)
 
  ### Fixed
 - Users only get tasks of datasets that they can access. [#4488](https://github.com/scalableminds/webknossos/pull/4488)

frontend/javascripts/oxalis/view/right-menu/trees_tab_view.js

@@ -322,7 +322,15 @@ class TreesTabView extends React.PureComponent<Props, State> {
   };
 
   showDeleteGroupModal = (id: number) => {
-    this.setState({ groupToDelete: id });
+    if (!this.props.skeletonTracing) return;
+
+    const { trees, treeGroups } = this.props.skeletonTracing;
+    const treeGroupToDelete = treeGroups.find(el => el.groupId === id);
+    const groupToTreesMap = createGroupToTreesMap(trees);
+
+    if (treeGroupToDelete && treeGroupToDelete.children.length === 0 && !groupToTreesMap[id])
+      this.deleteGroup(id);
+    else this.setState({ groupToDelete: id });
   };
 
   handleDelete = () => {