Restart proxy system only if it exists.

(cherry picked from commit e287d8c2056c96e0cd6cfad1d16eb210c07d9ddb)

bin/v-add-letsencrypt-domain

@@ -239,8 +239,10 @@ for auth in $authz; do
                 if [ ! -e "$sconf" ]; then
                     ln -s "$conf" "$sconf"
                 fi
-                $BIN/v-restart-proxy
-                check_result $? "Proxy restart failed" > /dev/null
+                if [ ! -z "$PROXY_SYSTEM" ]; then
+                    $BIN/v-restart-proxy
+                    check_result $? "Proxy restart failed" > /dev/null
+                fi
             else
                 # Get root directory from configuration
                 domain_config="$HOMEDIR/$user/conf/web/$domain"