tail: fix behaviour of tail -n0 in follow mode

[AnandajithS]

Fixed incorrect handling of tail -n0 -f in the bounded execution path.

Also added logic to handle the case where the file size is less than blksize_limit, which causes it to follow the unbounded execution path

Fixes #9102

[sylvestre]

Could you please add a test to make sure we don't regress in the future? Thanks

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/misc/tee (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

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

[github-actions]

GNU testsuite comparison:

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

[github-actions]

GNU testsuite comparison:

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

[github-actions]

GNU testsuite comparison:

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

[sylvestre]

please remove the unrelated changes

[codspeed-hq]

CodSpeed Performance Report

Merging #9114 will not alter performance

_{Comparing AnandajithS:fix_tail (9ce8ebb) with main (2d718f2)}

Summary

✅ 127 untouched
⏩ 6 skipped¹

Footnotes

1. 6 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[github-actions]

GNU testsuite comparison:

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

[AnandajithS]

@sylvestre It should be fixed now

[sylvestre]

sorry for the latency

[xtqqczze]

some CI runs for this PR are still queued!

https://github.com/uutils/coreutils/actions/runs/19142997114