Update 0452.用最少数量的箭引爆气球.md

Java code:
- Fix an error in sorting (simplified as well)
- Add checking for boundary condition

problems/0452.用最少数量的箭引爆气球.md

@@ -142,16 +142,8 @@ Java：
 ```java
 class Solution {
     public int findMinArrowShots(int[][] points) {
-        Arrays.sort(points, new Comparator<int[]>() {
-            @Override
-            public int compare(int[] o1, int[] o2) {
-                if (o1[0] != o2[0]) {
-                    return Integer.compare(o1[0],o2[0]);
-                } else {
-                    return Integer.compare(o1[0],o2[0]);
-                }
-            }
-        });
+        if (points.length == 0) return 0;
+        Arrays.sort(points, (o1, o2) -> Integer.compare(o1[0], o2[0]));
 
         int count = 1;
         for (int i = 1; i < points.length; i++) {