Uninitialized memory exposed by `write::Decoder` on a corrupt legacy frame

From 0.4.22 to 0.7.x, the writer behind zstd::stream::write::Decoder set its output buffer's length to its full capacity before each decompression call, then to the position the call reported, and only checked for an error afterwards. When decompression fails inside a legacy zstd v0.4 to v0.7...