Contact reporting may panic in assert

[Ughuuu]

In specific case where the contact is reported with same ID, there will be a panic that occurs:

Here you have an example that reproduces this: appsinacup/godot-rapier-physics#195

Issue happens here:

src/geometry/broad_phase_multi_sap/sap_utils.rs

pub(crate) fn sort2(a: u32, b: u32) -> (u32, u32) {
    assert_ne!(a, b);

    if a < b {
        (a, b)
    } else {
        (b, a)
    }
}

In my case a is 7 and b is 7.

This function is called from:

src/geometry/broad_phase_multi_sap/sap_axis.rs

Possibly best is to change calling function of this (eg. batch_insert or update_endpoints) to not insert or sort if the proxies are equal. If we do allow equal proxies, that will introduce issues down the line (there are other asserts that will fail).

There is already such an if in one of the 3 places where this function is used, eg.:

In batch_insert:

if endpoint2.proxy() == endpoint.proxy() {
    continue;
}

[Ughuuu]

Hm, no, if I do this if then some contacts are missed. Hm..

[Ughuuu]

Strange issue, seems to be related to me scaling a shape, which results in a box with negative width I think.