OSV-2021-1086 Heap-buffer-overflow in dwg_convert_SAB_to_SAT1

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=36728 Crash type: Heap-buffer-overflow READ 2 Crash state: dwgconvertSABtoSAT1 dxf3dsolid dwgdxfREGIONprivate...