[BUG] panic when multiple events are set in empty namespace

[heliosgo]

Describe the bug
When multiple events are set in empty namespace, and include OnNativeMessage, it may panic if received native message before connectedNamespaces is set.

Screenshots

Here is some source code I found.

func (c *Conn) handleMessage(msg Message) error {
	if msg.isInvalid {
		return ErrInvalidPayload
	}

	if msg.IsNative && c.allowNativeMessages {
		ns := c.Namespace("")
		return ns.events.fireEvent(ns, msg)               // panic
	}

	......

	return nil
}

I think the code should be like this.

func (c *Conn) handleMessage(msg Message) error {
	if msg.isInvalid {
		return ErrInvalidPayload
	}

	if msg.IsNative && c.shouldHandleOnlyNativeMessages {    // this line
		ns := c.Namespace("")
		return ns.events.fireEvent(ns, msg)         
	}

	......

	return nil
}