Fix an instance of `NULL + 0` in `ZSTD_decompressStream()`. Also, improve our `stream_decompress` fuzzer to pass `NULL` in/out buffers to `ZSTD_decompressStream()`, and fix 2 issues that were immediately surfaced. Fixes #3351
Fix an instance of `NULL + 0` in `ZSTD_decompressStream()`. Also, improve our `stream_decompress` fuzzer to pass `NULL` in/out buffers to `ZSTD_decompressStream()`, and fix 2 issues that were immediately surfaced. Fixes #3351