fix: clean file if no cnames are to be saved

imageroot/bin/reload_hosts

@@ -7,6 +7,7 @@
 
 import json
 import subprocess
+import os
 
 import agent
 import network
@@ -30,9 +31,12 @@ if 'interface' in config and config['interface'] != '':
 
     # save a new configuration file for dnsmasq, so that it can resolve the CNAMEs to the node fqdn
     redis_client = agent.redis_connect(use_replica=True)
+    hosts = redis_client.smembers(f'{agent.resolve_agent_id("traefik@node")}/hosts')
+    # if there are hosts, write them to the file
     with open("dnsmasq.d/01cnames.conf", "w") as file:
-        file.write("# This file is automatically generated by NethServer, manual changes will be lost.\n")
-        file.write('cname=')
-        for host in redis_client.smembers(f'{agent.resolve_agent_id("traefik@node")}/hosts'):
-            file.write(f'{host},')
-        file.write(f'{fqdn}\n')
+            file.write("# This file is automatically generated by NethServer, manual changes will be lost.\n")
+            if len(hosts) > 0:
+                file.write('cname=')
+                for host in hosts:
+                    file.write(f'{host},')
+                file.write(f'{fqdn}\n')