fix(top): handle stopped and paused containers correctly

[immanuwell]

nerdctl top silently exits 0 with no output for stopped and paused containers

Repro:

id=$(nerdctl run -d alpine sleep 300)
nerdctl stop "$id"
nerdctl top "$id"
echo $?

Before this prints nothing and exits 0. Pausing a running container has the same empty output

This returns is not running for stopped tasks and lets paused tasks reach the existing PID lookup.
Running containers stay unchanged.
Tests cover both cases with nerdctl and Docker

[AkihiroSuda]

Thanks