OSV-2021-398 Segv on unknown address in llvm_ks::StringRef::operator

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=30932 Crash type: Segv on unknown address Crash state: llvmks::StringRef::operator llvmks::HashString llvmks::StringMapImpl::LookupBucketFor...