qemu: Do not try to set memlock on inactive domain

qemu: Do not try to set memlock on inactive domain

When we call qemuDomainSetMaxMemLock to reset memory locking limit back
to its original value the domain can already be stopped (for example
after the domain shuts down during migration) in which case it does not
make sense to set any limit. Doing so can even be harmful as we may end
up setting the limit for the daemon itself as the PID is 0.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>