bin/57483: tail -fn +20 and -fc +20 broken by legacy format

[наб <nabijaczleweli%nabijaczleweli.xyz@localhost>]

>Number:         57483
>Category:       bin
>Synopsis:       tail -fn +20 and -fc +20 broken by legacy format
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Jun 23 14:20:00 +0000 2023
>Originator:     TODO
>Release:        NetBSD 9.2
>Environment:
System: NetBSD netbsd-dev 9.2 NetBSD 9.2 (GENERIC) #0: Wed May 12 13:15:55 UTC 2021 mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/i386/compile/GENERIC i386
Architecture: i386
Machine: i386
>Description:
Regardless of the inputs, tail -fc +20 and tail -fn +20 error
instantly with
  tail: illegal offset -- -n+20

This could have something to do with the undocumented "tail +20"
and "tail -20" legacy usages, but this breaks normal standard usage,
but tail -c +20 and tail -n +20 do work, so idk.

Best,

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>Fix:

Unknown
>Unformatted:
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