OSV-2020-2106 UNKNOWN READ in grk::SparseBuffer<6u, 6u>::read_or_write

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=26702 Crash type: UNKNOWN READ Crash state: grk::SparseBuffer::readorwrite grk::SparseBuffer::read bool grk::decompresspartialtile...