docs:补充0046Java代码的return语句

problems/0046.全排列.md

@@ -201,6 +201,7 @@ class Solution {
     public void backtrack(int[] nums, LinkedList<Integer> path) {
         if (path.size() == nums.length) {
             result.add(new ArrayList<>(path));
+            return;
         }
         for (int i =0; i < nums.length; i++) {
             // 如果path中已有，则跳过
@@ -524,3 +525,4 @@ public class Solution
 <a href="https://programmercarl.com/other/kstar.html" target="_blank">
   <img src="../pics/网站星球宣传海报.jpg" width="1000"/>
 </a>
+