[Web] found unexpected negative `PointerEvent.pointerId`, but the touch event comes through

Description

Hello. I get the following error when using touch events on Apple mobile devices.

Here are console logs from when I was testing on iPad:

For every touch event, I get the following errors in the console. Note the intended touch event coming through WindowEvent::PointerButton -> ButtonSource::Touch does get delivered to the fn window_event function of the ApplicationHandler, though it's just spammed with these errors as well.

The line of code causing the error is here:

https://github.com/rust-windowing/winit/blob/4d5e68c6e23d9633051ed9c1382eb8bd978751f1/src/platform_impl/web/event.rs#L1-L12

I tried looking into the W3C spec for PointerEvent.pointerId, and it doesn't give me the impression that this number can't be negative, though I'm not too familiar.

Tested browsers

Safari (newer than listed)

Tested devices

iPhone 12 (18.1.1)
iPad Pro (18.3)

Winit version

The latest master branch, which at the time of this issue is https://github.com/rust-windowing/winit/commit/4d5e68c6e23d9633051ed9c1382eb8bd978751f1.

Start in src/platform_impl/web/event.rs at the PointerEvent.pointerId handling linked in the issue. Reproduce the behavior on Safari using an iPhone or iPad touch event, then trace why the negative pointer ID is reported as an error. Done means touch events remain delivered to ApplicationHandler::window_event without the repeated erroneous errors.