copy evt.Codes to avoid concurrency issues

[devlikepro]

Right now in emitQRs function changes the original event, events.QR.
However, we send it already to other handlers, but we change it here.

In my case, I tried to JSON.Marshal(evt) and sometimes got reflect: slice index out of range concurrency error.

It looks like instead of changing evt.Codes we should copy it first and then change copied slice.

It's minor issue, but it's better not to change the values we already send outside, IMO.

Not sure if coping it before Marshal would help btw, because it'll be anyway concurrent access 🤔

[tulir]

It's probably easier to just not use the QR channel if you want to manage QR codes yourself 🤔

[devlikepro]

@tulir the main idea - if you send event outside it should have "concurrent" access to it, not be changed after you sent it.

You can close PR if you feel, fine for me!
We handled panic in JSON serialization, but I'd say it's good practice to avoid changing objects after sending it to consumers.

if you want to manage QR codes yourself

I don't, I love the way how qr channel does it.
I just wanted to dump all "events" from meow to JSON for troubleshooting/debug purpose.

[tulir]

The other problem is that the PR is implemented incorrectly

[devlikepro]

omg, you're right! It was an empty slice before 😨 Thank you for the fix! 🙇