Sometimes, calling JS_ToCString(ctx, val) where val is an instance of InternalError returns an empty string. Not very helpful when the exception object does in fact have a .message property with a human-readable error message.

Probably happens when there is a pending exception. Deep down, quickjs tries to invoke the [Symbol.toPrimitive] method but I doubt that works while an exception is pending.

Let's make debugging a little less miserable and special-case exception objects.