[Bug] crash in the aptos move coverage tool

[Rqnsom]

🐛 Bug

While performing some test with the move-mutation-tool, I encountered a crash here:

➜  aptos-framework git:(main) ✗ aptos move coverage source --module block
thread 'main' panicked at third_party/move/tools/move-coverage/src/source_coverage.rs:319:71:
attempt to subtract with overflow
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

To reproduce

cd aptos-core/aptos-move/framework/aptos-framework;
aptos move test --coverage;
aptos move coverage source --module block;
thread 'main' panicked at third_party/move/tools/move-coverage/src/source_coverage.rs:319:71:
attempt to subtract with overflow
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Stack trace/error message

$ aptos-framework git:(main) ✗ aptos move coverage source --module block
thread 'main' panicked at third_party/move/tools/move-coverage/src/source_coverage.rs:319:71:
attempt to subtract with overflow
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Expected Behavior

No crash. The coverage output is expected instead.

System information

Please complete the following information:

$ aptos-framework git:(main) ✗ aptos -V
aptos 4.2.3
$ uname -moprsv
Darwin 24.0.0 Darwin Kernel Version 24.0.0: Tue Sep 24 23:37:13 PDT 2024; root:xnu-11215.1.12~1/RELEASE_ARM64_T8112 arm64 arm
$ ➜  aptos-framework git:(main) ✗ rustc -V
rustc 1.78.0 (9b00956e5 2024-04-29)

[vineethk]

Related to #15117.