BUG: halog: fix broken output limitation

BUG: halog: fix broken output limitation

Commit 667c905f introduced parameter -m to halog which limits the size
of the output. Unfortunately it is completely broken in that it doesn't
check that the limit was previously set or not, and also prevents a
simple counting operation from returning anything if a limit is not set.

Note that the -gt and -pct outputs behave differently in face of this
limit, since they count the valid output lines BEFORE actually producing
the data, so the limit really applies to valid input lines.