fix(watch): avoid traversing non-plain objects

Author: yyx990803

packages/runtime-core/src/apiWatch.ts

@@ -18,7 +18,8 @@ import {
  NOOP,
  remove,
  isMap,
- isSet
+ isSet,
+ isPlainObject
 } from '@vue/shared'
 import {
  currentInstance,
@@ -391,9 +392,9 @@ function traverse(value: unknown, seen: Set<unknown> = new Set()) {
  value.forEach((v: any) => {
  traverse(v, seen)
  })
- } else {
+ } else if (isPlainObject(value)) {
  for (const key in value) {
- traverse(value[key], seen)
+ traverse((value as any)[key], seen)
  }
  }
  return value