OSV-2026-646 Heap-buffer-overflow in sentencepiece::unigram::Model::EncodeOptimized

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=507169860 Crash type: Heap-buffer-overflow READ 8 Crash state: sentencepiece::unigram::Model::EncodeOptimized sentencepiece::unigram::Model::Encode sentencepiece::SentencePieceProcessor::Encode...