Fix panic in mesh picking when a mesh is RENDER_WORLD only

[greeble-dev]

Objective

Fix a panic in mesh picking if a mesh is RenderAssetUsages::RENDER_WORLD only. The panic was reported in #22206, although that issue is framed as a broader concern and so is not resolved by this PR. The problem was introduced in #21732.

Solution

Changed mesh accesses to use the non-panicking try_ variants. This means extracted meshes are silently ignored as before.

I also did a quick scan to see if could spot any other engine crates that might have the same issue - didn't see any but could easily have missed one.

Testing

Tested by modifying the mesh_picking example:

+    let mut p = Mesh::from(Cuboid::default());
+    p.asset_usage = bevy_asset::RenderAssetUsages::RENDER_WORLD;
     let shapes = [
-        meshes.add(Cuboid::default()),
+        meshes.add(p),

[greeble-dev]

Adding to the 0.18 milestone - the reporting issue is tagged as 0.18, and the bug it fixes is a panic introduced in 0.18.

[kfc35]

LGTM for correctness, checked out this branch and verified that the example does not crash with this code

[robtfm]

code is fine.

to consider it properly closed i think we should warn_once! when the mesh data is extracted - something like

let positions = mesh
        .try_attribute_option(Mesh::ATTRIBUTE_POSITION) // only errors if extracted
        .inspect_err(|_| warn_once!("must use main world"))
        .ok()?? // else returns Ok(Option<Values>) so we must ?? to get the data out
        .as_float3()?;

or

let positions = match mesh.try_attribute(Mesh::ATTRIBUTE_POSITION) {
  Err(Extracted) => { warn_once!("extracted"); return None }
  Err(Missing) => { warn_once!("missing"); return None }
  Ok(data) => data.as_float3()?;
}