Fuzzer Failure

**Repro:**
```
bazel test -c opt //xls/fuzzer:run_crasher_test_2026-05-06_cbc5.x
```

**Error Message:**
```
E0506 02:22:20.707682 2325820 sample_runner.cc:831] Exception when running sample: INVALID_ARGUMENT: SampleError: Result miscompare for sample 46:
args: bits[1591]:0x0; bits[16]:0x8000
evaluated opt IR (JIT), evaluated opt IR (interpreter), evaluated unopt IR (interpreter), interpreted DSLX, simulated, simulated_ng =
(bits[4]:0x0, bits[360]:0x0, bits[4]:0xe)
evaluated unopt IR (JIT) =
(bits[4]:0x0, bits[360]:0x0, bits[4]:0xf)
== STACK ==
@ 0x7f76f15d66cc (xls::CompareResultsFunction())
@ 0x7f76f19f5f19 (xls::SampleRunner::RunFunction())
@ 0x7f76f19f0ad9 (xls::SampleRunner::RunFromFiles())
@ 0x7f76f32a44f2 (xls::RunSample())
@ 0x7f76f32a5e58 (xls::GenerateSampleAndRun())
@ 0x7f76f36b30dd (xls::(anonymous namespace)::FuzzIntegrationTest_Fuzzing_Test::TestBody())
@ 0x7f766043552a (testing::Test::Run())
@ 0x7f7660436dc3 (testing::TestInfo::Run())
@ 0x7f7660438117 (testing::TestSuite::Run())
@ 0x7f766044caed (testing::internal::UnitTestImpl::RunAllTests())
@ 0x7f766044b738 (testing::UnitTest::Run())
@ 0x7f76c42c99ef (main)
@ 0x7f760f1ddf12 (__libc_start_main)
@ 0x564edb444b2a (../sysdeps/x86_64/start.S:122 _start)
E0506 02:22:20.735444 2325820 run_fuzz.cc:278] Sample failed: INVALID_ARGUMENT: SampleError: Result miscompare for sample 46:
args: bits[1591]:0x0; bits[16]:0x8000
evaluated opt IR (JIT), evaluated opt IR (interpreter), evaluated unopt IR (interpreter), interpreted DSLX, simulated, simulated_ng =
(bits[4]:0x0, bits[360]:0x0, bits[4]:0xe)
evaluated unopt IR (JIT) =
(bits[4]:0x0, bits[360]:0x0, bits[4]:0xf)
=== Source Location Trace: ===
third_party/xls/fuzzer/cpp_sample_runner.cc:119
third_party/xls/fuzzer/run_fuzz.cc:233
```