Iterator: use hasNext() in method next() to reduce code redundancy

src/main/java/io/ad/structs/LinkedList.java

@@ -130,7 +130,7 @@ public class LinkedList<E> implements List<E> {
 	           return next!=null;
 	        }
 	        public E next() {
-	           if (next==null) throw new NoSuchElementException();
+	           if (!hasNext()) throw new NoSuchElementException();
 	           E value = next.data;
 	           next = next.next;
 	           return value;