OSV-2021-775 Heap-buffer-overflow in _m3d_safestr

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=34416 Crash type: Heap-buffer-overflow WRITE 1 Crash state: m3dsafestr m3dload Assimp::M3DWrapper::M3DWrapper...