refactor(set_ddns): replace recursion with while loop

scripts/menus/ddns.sh

@@ -33,6 +33,7 @@ EOF
 }
 
 set_ddns() {
+    while true; do
         echo "-----------------------------------------------"
         read -r -p "请输入你的域名 > " str
         [ -z "$str" ] && domain="$domain" || domain="$str"
@@ -58,9 +59,9 @@ set_ddns() {
         read -r -p "确认添加？(1/0) > " res
         if [ "$res" = 1 ]; then
             add_ddns
-    else
-        set_ddns
+            break
         fi
+    done
 }
 
 set_ddns_service() {