[BUG] fastjson2 兼容版本不能完全正确解析字符串

### 问题描述

fastjson2 兼容版本不能完全正确解析字符串

### 环境信息

- JDK信息： jdk 1.8.0_472
- 版本信息：Fastjson 2.0.60

### 重现步骤
*如何操作可以重现该问题：*

1. 使用 `JSONObject.parseObject()` 方法
2. 输入 `{19:2,29:1,39:3}` 数据
3. 字符串不能完全正确解析
```java
//部分关键代码
...
Map tabletopLevelMap = new HashMap<>();
JSONObject levelInfoMap = JSONObject.parseObject("{19:2,29:1,39:3}");
for (Map.Entry entry : levelInfoMap.entrySet()) {
tabletopLevelMap.put(Integer.parseInt(entry.getKey()), (Integer) entry.getValue());
}
...
int count = 0;
for (Map.Entry entry : tabletopLevelMap.entrySet()) {
if (entry.getValue() >= needLevel) {
count += 1;
}
}
return count;
...
```

Start with JSONObject.parseObject() and reproduce the issue using the input {19:2,29:1,39:3} under JDK 1.8.0_472 and Fastjson 2.0.60. Trace the compatibility parsing result and add a regression check; done means the input is parsed completely so its numeric keys and values can be iterated as shown.

Written by the indexing model from the issue text.