Fix security issues

Fixes GHSA-2w6w-674q-4c4q, GHSA-xhpv-hc6g-r9c6, GHSA-3mfm-83xf-c92r, GHSA-2qvq-rjwj-gvw9, GHSA-9cx6-37pm-9jff, GHSA-7rx3-28cr-v5wh, GHSA-442j-39wm-28r2, GHSA-xjpj-3mr7-gcpf

lib/handlebars/compiler/javascript-compiler.js

@@ -686,9 +686,18 @@ JavaScriptCompiler.prototype = {
     let foundDecorator = this.nameLookup('decorators', name, 'decorator'),
       options = this.setupHelperArgs(name, paramSize);
 
+    // Store the resolved decorator in a variable and verify it is a function before
+    // calling it. Without this, unregistered decorators can cause an unhandled TypeError
+    // (calling undefined), which crashes the process — enabling Denial of Service.
+    this.decorators.push(['var decorator = ', foundDecorator, ';']);
+    this.decorators.push([
+      'if (typeof decorator !== "function") { throw new Error(',
+      this.quotedString('Missing decorator: "' + name + '"'),
+      '); }'
+    ]);
     this.decorators.push([
       'fn = ',
-      this.decorators.functionCall(foundDecorator, '', [
+      this.decorators.functionCall('decorator', '', [
         'fn',
         'props',
         'container',