Only create inadyn config file if it doesn't exist

src/freedombone-utils-web

@@ -535,9 +535,11 @@ function install_dynamicdns {
     fi
 
     # create a configuration file
-    { echo 'period          = 300';
-      echo 'user-agent      = Mozilla/5.0';
-      echo ''; } > "${INADYN_CONFIG_FILE}"
+    if [ ! -f "${INADYN_CONFIG_FILE}" ]; then
+        { echo 'period          = 300';
+          echo 'user-agent      = Mozilla/5.0';
+          echo ''; } > "${INADYN_CONFIG_FILE}"
+    fi
     chmod 600 "${INADYN_CONFIG_FILE}"
 
     { echo '[Unit]';