fix: Update linkedlist_deque.cpp (#1062)

There is something error when delete node, should 'delete front' or 'delete rear' outside the body of if cycle.

codes/cpp/chapter_stack_and_queue/linkedlist_deque.cpp

@@ -92,8 +92,8 @@ class LinkedListDeque {
             if (fNext != nullptr) {
                 fNext->prev = nullptr;
                 front->next = nullptr;
-                delete front;
             }
+            delete front;
             front = fNext; // 更新头节点
         // 队尾出队操作
         } else {
@@ -103,8 +103,8 @@ class LinkedListDeque {
             if (rPrev != nullptr) {
                 rPrev->next = nullptr;
                 rear->prev = nullptr;
-                delete rear;
             }
+            delete rear;
             rear = rPrev; // 更新尾节点
         }
         queSize--; // 更新队列长度