Add cycle-checking for `JsrValue` constructor (to avoid SOE)

[dantesun]

I am sorry but I can't provide more information. My guess this error happend when using JSON.asString to serialize a JsrValue object. The jackson-jr version is 2.11.2.

java.lang.StackOverflowError
	at com.fasterxml.jackson.jr.private_.json.WriterBasedJsonGenerator.writeStartObject(WriterBasedJsonGenerator.java:296)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter.writeBeanValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.BeanWriter.writeValue(BeanWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter._writeValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter.writeBeanValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.BeanWriter.writeValue(BeanWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter._writeValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter.writeBeanValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.BeanWriter.writeValue(BeanWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter._writeValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter.writeBeanValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.BeanWriter.writeValue(BeanWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter._writeValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter.writeBeanValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.BeanWriter.writeValue(BeanWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter._writeValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter.writeBeanValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.BeanWriter.writeValue(BeanWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter._writeValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter.writeBeanValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.BeanWriter.writeValue(BeanWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter._writeValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter.writeBeanValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.BeanWriter.writeValue(BeanWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter._writeValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter.writeBeanValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.BeanWriter.writeValue(BeanWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter._writeValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter.writeBeanValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.BeanWriter.writeValue(BeanWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter._writeValue(JSONWriter.java)
	at com.fasterxml.jackson.jr.ob.impl.JSONWriter.writeBeanValue(JSONWriter.java)

[cowtowncoder]

This would likely result from a cyclic data structure; those can not be serialized by jackson-jr.
If this is not the root cause, it would be necessary to have a reproduction.

[dantesun]

Please considering add 'clone' support for JrsValue. The current constructor of JrsObject will not check for cyclic data structure.

    public JrsObject(Map<String, JrsValue> values) {
        _values = values;
    }

[cowtowncoder]

I will leave this as an RFE, in case someone has an idea of implementation.
Implementing support for cyclic data structures is usually a bit complicated thing to do (and tends to add processing overhead due to state keeping required) so this is unlikely to get implemented without contribution.