crash on `std`

I am getting a crash on std (I might be doing something obvious wrong) -- here is the output below.

Possibly related to #58

cargo run --bin scan ../rust/library/std    
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.20s
     Running `target/debug/scan ../rust/library/std`
[2024-07-08T20:22:29Z WARN  cargo_scan::scan_stats] Scan crashed, skipping crate: ../rust/library/std
crate, fn_decl, callee, effect, dir, file, line, col

num_effects, total, loc_lb, loc_ub, macros, loc_lb, loc_ub, conditional_code, loc_lb, loc_ub, skipped_calls, loc_lb, loc_ub, skipped_fn_ptrs, loc_lb, loc_ub, skipped_other, loc_lb, loc_ub, unsafe_trait, loc_lb, loc_ub, unsafe_impl, loc_lb, loc_ub, pub_fns, pub_fns_with_effects, pub_total_effects, audited_fns, audited_loc
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

Reproduce the failure with cargo run --bin scan ../rust/library/std and inspect the scan entry point and crash output, comparing the behavior with issue #58. Done means scanning Rust's std completes without the crash and produces meaningful scan statistics instead of the zeroed output.