hotfix(tail): skip events for untracked files in follow mode

[naoNao89]

Hotfix for CI #9437 #9628 #9629 #9587

Fixes test_retry6 failure by skipping file watcher events for untracked files in --follow=descriptor mode. When using tail -f without --retry, missing files that appear later should not be monitored. Added guard in handle_event() to prevent accessing untracked files in the map.

https://github.com/uutils/coreutils/actions/runs/20111856793/job/57711065899?pr=9437 https://github.com/uutils/coreutils/actions/runs/20111856782/job/57711461006?pr=9437 https://github.com/uutils/coreutils/actions/runs/20113818498/job/57718649412?pr=9629 https://github.com/uutils/coreutils/actions/runs/20113818498/job/57718649412?pr=9629 https://github.com/uutils/coreutils/actions/runs/20109296480/job/57703320639?pr=9628 https://github.com/uutils/coreutils/actions/runs/20113542716/job/57717579129?pr=9587

[github-actions[bot]]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)

[github-actions[bot]]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/tail/inotify-dir-recreate is now passing!

[github-actions[bot]]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/tail/inotify-dir-recreate is now passing!