virsh-network: Resolve Coverity RESOURCE_LEAK

Need to free 'xmlFromFile' on/for the error path when current was
returning false only

tools/virsh-network.c

@@ -974,7 +974,7 @@ cmdNetworkUpdate(vshControl *ctl, const vshCmd *cmd)
     if (current) {
         if (live || config) {
             vshError(ctl, "%s", _("--current must be specified exclusively"));
-            return false;
+            goto cleanup;
         }
         flags |= VIR_NETWORK_UPDATE_AFFECT_CURRENT;
     } else {