After render fail "warn" cause "InternalError: too much recursion" if one of props is PublicInstanceProxyHandlers

[wszerad]

Version

3.0.0-beta.5

Reproduction link

https://jsfiddle.net/24hun8ay/2/

Steps to reproduce

just run code

What is expected?

Normal warninig: "can't access property "a", a.a is undefined"

What is actually happening?

We get: "InternalError: too much recursion"

---

1. "warn" function uses "formatProp" to format warning output
2. "formatProp" checks type of prop by looking for "_isRef" field
3. prop is a PublicInstanceProxyHandlers so when target doesn't contain such field we get warn again, go to 1.

[ysj16]

The state will be covered by ref in setRef-L1930(I wonder the reason for that), and then will call warn in componentProxy recursively. @yyx990803