rpc: avoid crashing in pre-exec if no workers are present

If max_workers is set to zero, then the worker thread pool won't be
created, so when serializing state for pre-exec we must set various
parameters to zero.
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>
Reviewed-by: NJim Fehlig <jfehlig@suse.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

src/rpc/virnetserver.c

@@ -580,18 +580,21 @@ virJSONValuePtr virNetServerPreExecRestart(virNetServerPtr srv)
         goto error;
 
     if (virJSONValueObjectAppendNumberUint(object, "min_workers",
+                                           srv->workers == NULL ? 0 :
                                            virThreadPoolGetMinWorkers(srv->workers)) < 0) {
         virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                        _("Cannot set min_workers data in JSON document"));
         goto error;
     }
     if (virJSONValueObjectAppendNumberUint(object, "max_workers",
+                                           srv->workers == NULL ? 0 :
                                            virThreadPoolGetMaxWorkers(srv->workers)) < 0) {
         virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                        _("Cannot set max_workers data in JSON document"));
         goto error;
     }
     if (virJSONValueObjectAppendNumberUint(object, "priority_workers",
+                                           srv->workers == NULL ? 0 :
                                            virThreadPoolGetPriorityWorkers(srv->workers)) < 0) {
         virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                        _("Cannot set priority_workers data in JSON document"));