Fix unused variable warnings in fuzzing build mode without asserts
Fix unused variable warnings in fuzzing build mode without asserts

Fix unused vairable warnings when `FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION` is defined but asserts are disabled.

Fixes #2210.

Cyan4973/zstd,Cyan4973/zstd,Cyan4973/zstd,Cyan4973/zstd,Cyan4973/zstd