Fuzzer failure, crasher 85f2.x

To repro:

```
bazel test -c opt //xls/fuzzer:run_crasher_test_2026-04-08_85f2
```

Error message:

```
Error: ABORTED: SystemVerilog assert failed at top.sv:379: Selector concat.406 was expected to be one-hot, and is not.
```