panic: "attempt to subtract with overflow" during readdir of snapshot directory

[asomers]

I mounted a FreeBSD 15.0-CURRENT VM's os disk with fuse-ufs. Running "ls /mnt/.snap" crashed the fuse server .

thread 'main' panicked at src/ufs.rs:374:19:
attempt to subtract with overflow
stack backtrace:
   0: rust_begin_unwind
             at /rustc/2c93fabd98d2c183bcb3afed1f7d51b2517ac5ed/library/std/src/panicking.rs:662:5
   1: core::panicking::panic_fmt
             at /rustc/2c93fabd98d2c183bcb3afed1f7d51b2517ac5ed/library/core/src/panicking.rs:74:14
   2: core::panicking::panic_const::panic_const_sub_overflow
             at /rustc/2c93fabd98d2c183bcb3afed1f7d51b2517ac5ed/library/core/src/panicking.rs:181:21
   3: fuse_ufs::ufs::readdir_block
             at ./src/ufs.rs:374:13
   4: fuse_ufs::ufs::Ufs::readdir
             at ./src/ufs.rs:243:12
   5: <fuse_ufs::ufs::Ufs as fuser::Filesystem>::readdir::{{closure}}
             at ./src/ufs.rs:480:4
   6: core::ops::function::FnOnce::call_once
             at /rustc/2c93fabd98d2c183bcb3afed1f7d51b2517ac5ed/library/core/src/ops/function.rs:250:5
   7: fuse_ufs::ufs::run
             at ./src/ufs.rs:335:2
   8: <fuse_ufs::ufs::Ufs as fuser::Filesystem>::readdir
             at ./src/ufs.rs:490:9
   9: fuser::request::Request::dispatch_req
             at /home/somers/.cargo/registry/src/index.crates.io-6f17d22bba15001f/fuser-0.14.0/src/request.rs:364:17
  10: fuser::request::Request::dispatch
             at /home/somers/.cargo/registry/src/index.crates.io-6f17d22bba15001f/fuser-0.14.0/src/request.rs:57:25
  11: fuser::session::Session<FS>::run
             at /home/somers/.cargo/registry/src/index.crates.io-6f17d22bba15001f/fuser-0.14.0/src/session.rs:135:34
  12: fuser::mount2::{{closure}}
             at /home/somers/.cargo/registry/src/index.crates.io-6f17d22bba15001f/fuser-0.14.0/src/lib.rs:1017:78
  13: core::result::Result<T,E>::and_then
             at /rustc/2c93fabd98d2c183bcb3afed1f7d51b2517ac5ed/library/core/src/result.rs:1346:22
  14: fuser::mount2
             at /home/somers/.cargo/registry/src/index.crates.io-6f17d22bba15001f/fuser-0.14.0/src/lib.rs:1017:5
  15: fuse_ufs::main
             at ./src/main.rs:24:2
  16: core::ops::function::FnOnce::call_once
             at /rustc/2c93fabd98d2c183bcb3afed1f7d51b2517ac5ed/library/core/src/ops/function.rs:250:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.