signalling a system doesn't set an error code on an error

[midnightveil]

Compare e.g.:

$ mq.sh sem -wait odroidc4_1
Attempting to grab lock you already own with the same key. Please explicitly release
Failed to acquire lock for system (odroidc4_1)
$ echo $?
2

With

$ mq.sh sem -signal odroidc4_1
Attempting to unlock system odroidc4_1 that you do not hold
$ echo $?
0

Or

$ mq.sh sem -signal odroidc4_1
Attempting to unlock system odroidc4_1 with the wrong key!
$ echo $?
0