fix: zero-initialize C++ arrays in documentation (#1936)

Explicitly initialize the array elements to 0 to eliminate potential undefined behavior.

docs/chapter_array_and_linkedlist/array.md

@@ -23,10 +23,10 @@
     ```cpp title="array.cpp"
     /* 初始化数组 */
     // 存储在栈上
-    int arr[5];
+    int arr[5] = {};
     int nums[5] = { 1, 3, 2, 5, 4 };
     // 存储在堆上（需要手动释放空间）
-    int* arr1 = new int[5];
+    int* arr1 = new int[5] {};
     int* nums1 = new int[5] { 1, 3, 2, 5, 4 };
     ```