certctl: Convert line endings before inspecting files.

[des]

Summary

This ensures that certificate files or bundles with DOS or Mac line
endings are recognized as such and handled identically to those with
Unix line endings.

PR: 274952

[allanjude]

reviewed-by: allanjude

[michaelo]

While technically I have no objection, I still consider that the split approach is wrong as layed out in the PR: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=274952