OSV-2020-1404 Use-of-uninitialized-value in LosslessReduceDepthOK

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=22581 Crash type: Use-of-uninitialized-value Crash state: LosslessReduceDepthOK ReadOneMNGImage ReadMNGImage...