Files
systemd/src/systemctl
Mike Yuan 8f9acf8e10 systemctl-show: make show_memory_available cover memory_available itself
Follow-up for f380473edf

This cleans up the code a bit. Also, before this commit,
if MemoryAvailable is set but show_memory_available
is false, and we have nothing else to output, empty
parenthesis is shown. This can be easily reproduced
on -.slice:

> systemctl status -- -.slice
> ...
> Memory: 1.8G ()
> ...
2024-05-08 21:20:05 +02:00
..
2024-04-03 11:50:25 +01:00