OSV-2020-360 Heap-use-after-free in read_chunks_after_idat

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=16081 Crash type: Heap-use-after-free READ Crash state: readchunksafteridat spngdecodeimage spngreadfuzzer.cc...