Check that monkeysphere server keys exist

src/freedombone-controlpanel-user

@@ -822,6 +822,10 @@ function menu_admin {
 }
 
 function sign_keys {
+	if [ ! -f /home/$USER/.monkeysphere/server_keys ]; then
+		return
+	fi
+
 	dialog --title $"Monkeysphere sign server keys" \
 		   --backtitle $"Freedombone Security Configuration" \
 		   --defaultno \