APNs: log invalid device tokens, rather than sending them

[rk-for-zulip]

APNs device tokens, as received through out iOS notifications library,
should be a hex string. Unfortunately, they're sometimes being sent to
the server as "[Object object]".

This is most likely due to the argument of handleDeviceToken
actually being an object, despite its typing as string, and being
improperly stringified by encodeParamsForUrl. However, it may
alternatively be the case that someone is mis-stringifying the object
before we get ahold of it, so log that case too.

This is work toward the resolution of #3672.

[rk-for-zulip]

⚠️ This PR is untested, due to the difficulty (noted elsewhere) of testing iOS notifications code.

[gnprice]

Thanks @ray-kraesig ! This should be helpful.

One style comment below.

[gnprice]

Let's write this error path in the early-return pattern:

  if (isBad(thing)) {
    logging.error('Thing is bad', { thing });
    return;
  }

  processNormally(thing);

This keeps the code that handles each error next to the code that tests for it. A related effect is that it helps the reader to study the behavior in a given error case, or the behavior in the "normal"/happy case, or to understand the full behavior by divide-and-conquer.

Doesn't hugely matter for a function this short with just one error case. But it's good to have the pattern consistent for if the function grows, or if another contributor copies the pattern in another context. And even at this scale I think it already helps.

[rk-for-zulip]

(I actually did write it that way in the first draft; I switched to the above because the negated logic seemed more straightforward.)

[gnprice]

Cool. Yeah, I think the main thing that can make this nested style appealing is that it lets you write down the things that are true in the happy path, rather than the things that aren't.

But then I think the effect on the code's overall structure generally ends up outweighing that, even at this scale.

Thanks for the revision!

[rk-for-zulip]

Done. Also, more honesty about being dishonest about types.

[gnprice]

Thanks -- merged!