cut: honor only-delimited in newline-delimiter mode

[can1357]

uutils cut routes -z -d '' through a special newline-delimiter code path that ignores the -s only-delimited flag. GNU still suppresses undelimited records in this mode, but uutils emits the whole record plus NUL.

Reproduction Steps

printf 'abc' | cut -z -d '' -s -f 1 | od -An -tx1
# Expected (GNU): no output bytes
# Actual (uutils): 61 62 63 00

Impact

Pipelines that rely on cut -s to drop undelimited records process data that should be filtered out.