Fix missing Ampersand

Uebung 2/Uebung2_2/doublyLinkedList.cpp

@@ -62,7 +62,7 @@ void DoublyLinkedList::append(DoublyLinkedList *appendingList) {
 }
 
 void DoublyLinkedList::splice(DoublyLinkedList *insertingList, int position) {
-  if (insertingList->head != NULL & insertingList->tail != NULL) {
+  if (insertingList->head != NULL && insertingList->tail != NULL) {
     ExtendedListItem *prev = NULL;
     ExtendedListItem *current = NULL;
     current = this->head;