Explicitly allow wrapping when decoding mid-side
Explicitly allow wrapping when decoding mid-side

This does not happen for valid FLAC files. For invalid files, we may
decode garbage, but that does not mean the application should crash in
debug mode. (Rust panics on overflow in debug mode.)

There were multiple overflows here, all detected by libfuzzer with
cargo-fuzz.

ruuda/claxon,ruuda/claxon,ruuda/claxon