Corrected a null pointer exception when linked list has only one element

Author: Suvradippaul

Diff for: lectures/18-linkedlist/code/src/com/kunal/CLL.java

@@ -28,7 +28,9 @@ public void display() {
         if (head != null) {
             do {
                 System.out.print(node.val + " -> ");
-                node = node.next;
+                if (node.next != null) {
+		    node = node.next;
+		}
             } while (node != head);
         }
         System.out.println("HEAD");