Fixes NetworkTree + - symbols not being displayed on first opening

src/main/java/de/tu_darmstadt/tk/SmartHomeNetworkSim/view/popups/NetworkTreePanel.java

@@ -130,6 +130,11 @@ public class NetworkTreePanel extends JScrollPane implements Observer {
 		this.controller = controller;
 		network = this.controller.getNetworkController();
 		networkTreeSettings = controller.getSettingsController().getNetworkTreeSettingsController();
+
+		//Adds + - as icons for expanding and collapsing the tree
+		UIManager.put("Tree.expandedIcon",  new ImageIcon(Utility.loadFile("images/treeMinus.gif")));
+		UIManager.put("Tree.collapsedIcon", new ImageIcon(Utility.loadFile("images/treePlus.gif")));
+		
 		tree = new JTree();
 		initializeRightClickMenu();
 
@@ -254,10 +259,6 @@ public class NetworkTreePanel extends JScrollPane implements Observer {
 			}
 		});
 		
-		//Adds + - as icons for expanding and collapsing the tree
-		UIManager.put("Tree.expandedIcon",  new ImageIcon(Utility.loadFile("images/treeMinus.gif")));
-		UIManager.put("Tree.collapsedIcon", new ImageIcon(Utility.loadFile("images/treePlus.gif")));
-		
 		update(null, null);
 	}