Auto merge of #158002 - bushrat011899:get_module_children_unwrap, r=oli-obk

Fix(ICE): Remove `unwrap` from `get_module_children`

# Objective

Fix an ICE I ran into while developing rust-lang/rust-clippy#17252 that stems from `rustc_metadata::rmeta::decoder::CrateMetadata::get_module_children` calling `unwrap`. The local value `non_reexports` can be `None` when the passed in `DefIndex` is for a non-module-like item. The documentation for `get_module_children` *implies* that it must only be called with module-like item indices, however it seems to me that it would be appropriate to just return nothing when called on a non-module-like item (if it isn't module-like, it has zero children).

## Solution

- Switched from an `Option::unwrap` to an `if let Some(...)`

---

## Notes

* No AI tooling of any kind was used during the creation of this PR.
* Please see [Zulip](https://rust-lang.zulipchat.com/#narrow/channel/122651-general/topic/.E2.9C.94.20.60rustc.60.20ICE.20from.20.60TyCtxt.3A.3Amodule_children.60/with/603700184) for some discussion.
* Please see this [failed Clippy CI run](https://github.com/rust-lang/rust-clippy/actions/runs/27596428127/job/81587609898#step:5:1) for an example of the ICE caused.

Author: bors

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -1287,8 +1287,10 @@ impl CrateMetadata {
             } else {
                 // Iterate over all children.
                 let non_reexports = self.root.tables.module_children_non_reexports.get(self, id);
-                for child_index in non_reexports.unwrap().decode((self, tcx)) {
-                    yield self.get_mod_child(tcx, child_index);
+                if let Some(non_reexports) = non_reexports {
+                    for child_index in non_reexports.decode((self, tcx)) {
+                        yield self.get_mod_child(tcx, child_index);
+                    }
                 }
 
                 let reexports = self.root.tables.module_children_reexports.get(self, id);