V6.x crash with illegal spread as single arrow parameter


* **Version**: 6.10.1
* **Platform**: Linux
* **Subsystem**: V8

Repro: `node -e "(...[42]) => 42"`

Fix: https://github.com/v8/v8/commit/b9f682baafb8fee8cca154d6dd66359facc06a69
I found this while investigating https://github.com/nodejs/node/issues/11977