Remove unused node groups when material is deleted

Sources/arm/ui/TabMaterials.hx

@@ -145,6 +145,7 @@ class TabMaterials {
 								materials.splice(i, 1);
 								UISidebar.inst.hwnd1.redraws = 2;
 								for (m in Project.materials) updateMaterialPointers(m.canvas.nodes, i);
+								for (n in m.canvas.nodes) UINodes.onNodeRemove(n);
 							}
 
 							var baseHandle = Id.handle().nest(m.id, {selected: m.paintBase});

Sources/arm/ui/UINodes.hx

@@ -190,7 +190,7 @@ class UINodes {
 		}
 	}
 
-	function onNodeRemove(node: TNode) {
+	public static function onNodeRemove(node: TNode) {
 		if (node.type == "GROUP") { // Remove unused groups
 			var found = false;
 			var canvases: Array<TNodeCanvas> = [];