Detect, warn and gracefully handle corrupt cells in lookup_arrow

[Wumpf]

lookup_arrow called arrow's slice which is defined to panic on out of bounds slices.

example code that would create such an entity

    // And some points in front of the rectangle.
    MsgSender::new("2d_layering/points_between_top_and_middle")
        .with_timepoint(sim_time(1 as _))
        .with_component(
            &(0..256).map(|i| Point2D::new(...).collect::<Vec<_>>(),
        )?
        .with_component(&[DrawOrder(1.51)])?
        .send(rec_stream)?;

Checklist

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PR Build Summary: https://build.rerun.io/pr/2055

[jprochazk]

From what I can tell, this will prevent the panic, but I don't understand any other consequences of making this change, so not sure if my review here is good enough to merge this! 🙂