GHSA-FPMH-FRQ8-7RJ8 compress zstd: Panic on two-block frames

Summary A crafted 27 KB two-block zstd frame makes DecodeAll and the streaming decoder panic with an out-of-range slice index instead of returning a decode error. The same bytes decode fine with the reference zstd. Any program that decompresses untrusted zstd input can be crashed by it. Reproduce...