OSV-2020-1380 Use-of-uninitialized-value in stbi__jpeg_decode_block_prog_ac

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=22589 Crash type: Use-of-uninitialized-value Crash state: stbijpegdecodeblockprogac stbiparseentropycodeddata stbidecodejpegimage...