virsh: don't list unknown domains

When the list of domains is fetched and being printed, but in the
meantime one domain was undefined before its status was fetched, the
output then includes domain with "no state".  With this patch, such
domain is skipped over as consecutive 'virsh list --all' (or the same
one ran a second later) wouldn't list it anyway.

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>

tools/virsh-domain-monitor.c

@@ -1916,6 +1916,11 @@ cmdList(vshControl *ctl, const vshCmd *cmd)
             ignore_value(virStrcpyStatic(id_buf, "-"));
 
         state = vshDomainState(ctl, dom, NULL);
+
+        /* Domain could've been removed in the meantime */
+        if (state < 0)
+            continue;
+
         if (optTable && managed && state == VIR_DOMAIN_SHUTOFF &&
             virDomainHasManagedSaveImage(dom, 0) > 0)
             state = -2;