fix: problem when watchUntil is run for the first time (#62)

Co-authored-by: huang yao <5945154+kirakiray@users.noreply.github.com>

Author: kirakiray

dist/stanz.js

@@ -1,4 +1,4 @@
-//! stanz - v8.1.26 https://github.com/kirakiray/stanz  (c) 2018-2024 YAO
+//! stanz - v8.1.27 https://github.com/kirakiray/stanz  (c) 2018-2024 YAO
 (function (global, factory) {
   typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
   typeof define === 'function' && define.amd ? define(factory) :
@@ -320,13 +320,18 @@
     },
     watchUntil(func) {
       return new Promise((resolve) => {
-        const tid = this.watch(() => {
-          const bool = func();
-          if (bool) {
-            this.unwatch(tid);
-            resolve(this);
-          }
-        });
+        let f;
+        const tid = this.watch(
+          (f = () => {
+            const bool = func();
+            if (bool) {
+              this.unwatch(tid);
+              resolve(this);
+            }
+          })
+        );
+
+        f();
       });
     },
   };