Fixes Pasting NullPointer, when mouse isn't on Canvas

src/ui/view/GUI.java

@@ -622,6 +622,7 @@ public class GUI implements CategoryListener {
 						}
 					}
 
+					if(tabTemp == null)return;
 					JScrollPane scrollPane = getScrollPaneFromTabbedPane();
 					Component canvasOrUpperNodeCanvas = scrollPane
 							.getViewport().getComponent(0);