(from https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=32371 )

The following reproducer:

import java.util.Base64;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONException;

public class FastJsonCrash {
    public static String btoa(String base64) {
        return new String(Base64.getDecoder().decode(base64));
    }
    public static void main(String[] args) {
        try {
            JSON.parse(btoa("ewogICAgICJzdGFvbnMiOiBbCiAgICAgewogICAgICIkcmVmIjogIi4gICJocmVmIi97VA=="));
        } catch (JSONException unused) {
        }
    }
}

throws this exception with the current master branch of fastjson:

java.lang.StringIndexOutOfBoundsException: String index out of range: 3
	at java.base/java.lang.StringLatin1.charAt(StringLatin1.java:48)
	at java.base/java.lang.String.charAt(String.java:709)
	at com.alibaba.fastjson.JSONPath$JSONPathParser.next(JSONPath.java:911)
	at com.alibaba.fastjson.JSONPath$JSONPathParser.skipWhitespace(JSONPath.java:1038)
	at com.alibaba.fastjson.JSONPath$JSONPathParser.readName(JSONPath.java:1904)
	at com.alibaba.fastjson.JSONPath$JSONPathParser.readSegement(JSONPath.java:983)
	at com.alibaba.fastjson.JSONPath$JSONPathParser.explain(JSONPath.java:1975)
	at com.alibaba.fastjson.JSONPath.init(JSONPath.java:87)
	at com.alibaba.fastjson.JSONPath.isRef(JSONPath.java:94)
	at com.alibaba.fastjson.parser.DefaultJSONParser.parseObject(DefaultJSONParser.java:458)
	at com.alibaba.fastjson.parser.DefaultJSONParser.parseArray(DefaultJSONParser.java:1246)
	at com.alibaba.fastjson.parser.DefaultJSONParser.parseObject(DefaultJSONParser.java:533)
	at com.alibaba.fastjson.parser.DefaultJSONParser.parse(DefaultJSONParser.java:1427)
	at com.alibaba.fastjson.parser.DefaultJSONParser.parse(DefaultJSONParser.java:1393)
	at com.alibaba.fastjson.JSON.parse(JSON.java:181)
	at com.alibaba.fastjson.JSON.parse(JSON.java:191)
	at com.alibaba.fastjson.JSON.parse(JSON.java:147)
	at FastJsonCrash.main(FastJsonCrash.java:12)