Ignore symlinks that point to nonexistent targets

[egibs]

We attempt to evaluate symlinks when recursively scanning for files in a given scan path; however, this tends to pollute output when the symlinks point to targets that don't exist.

For example, -compat packages are essentially a collection of symlinks but the target is not installed as part of the package:

/ # apk add opentofu-1.8-compat
(1/1) Installing opentofu-1.8-compat (1.8.6-r0)
OK: 790 MiB in 50 packages
...
/ # ls -hal /usr/local/bin/ | grep tofu
lrwxrwxrwx    1 root     root          17 Nov 27 14:03 opentofu -> /usr/bin/opentofu
/ # ls /usr/bin/opentofu
ls: /usr/bin/opentofu: No such file or directory

Scanning this file fails:

/workspace # go run cmd/mal/mal.go analyze /usr/local/bin/opentofu
🔎 Scanning "/usr/local/bin/opentofu"
💣 find: eval "/usr/local/bin/opentofu": lstat /usr/bin/opentofu: no such file or directory
exit status 2

Instead, this PR returns gracefully when this is the case and logs the error instead:

/workspace # go run cmd/mal/mal.go analyze /usr/local/bin/opentofu
🔎 Scanning "/usr/local/bin/opentofu"
...
/workspace # go run cmd/mal/mal.go --verbose analyze /usr/local/bin/opentofu
🔎 Scanning "/usr/local/bin/opentofu"
time=2024-11-27T14:06:28.289Z level=INFO source=/workspace/pkg/action/scan.go:49 msg="symlink target does not exist: lstat /usr/bin/opentofu: no such file or directory"