OSV-2020-1516 Use-of-uninitialized-value in ScaleQuantumToChar

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=22583 Crash type: Use-of-uninitialized-value Crash state: ScaleQuantumToChar LosslessReduceDepthOK ReadOneMNGImage...