qemu: hotplug: Fix the condition check for net->downscript

According to the context, here we are checking net->downscript's validity,
Signed-off-by: NLiao Pingfang <liao.pingfang@zte.com.cn>
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>

src/qemu/qemu_hotplug.c

@@ -4673,8 +4673,8 @@ qemuDomainRemoveNetDevice(virQEMUDriverPtr driver,
         else
             VIR_WARN("Unable to release network device '%s'", NULLSTR(net->ifname));
     } else if (net->type == VIR_DOMAIN_NET_TYPE_ETHERNET) {
-        if (net->script)
-           virNetDevRunEthernetScript(net->ifname, net->downscript);
+        if (net->downscript)
+            virNetDevRunEthernetScript(net->ifname, net->downscript);
     }
     virDomainNetDefFree(net);
     return 0;