dom0/qvm-ls: don't crash when multiple options given

dom0/qvm-tools/qvm-ls

@@ -130,11 +130,14 @@ def main():
         fields_to_display += ["mem"]
 
     if (options.network):
+        if 'template' in fields_to_display:
             fields_to_display.remove ("template")
         fields_to_display += ["ip", "netmask", "gateway"]
 
     if (options.disk):
+        if 'template' in fields_to_display:
             fields_to_display.remove ("template")
+        if 'netvm' in fields_to_display:
             fields_to_display.remove ("netvm")
         fields_to_display += ["priv-curr", "priv-max", "root-curr", "root-max", "disk" ]