AG-18132 handle getScriptletFunction calls on unknown scriptlet names

Merge in ADGUARD-FILTERS/scriptlets from fix/AG-18132 to release/v1.8

Squashed commit of the following:

commit 0beb472
Merge: 481ed62 7fd04c9
Author: Stanislav A <s.atroschenko@adguard.com>
Date:   Mon Dec 19 19:55:37 2022 +0300

    Merge branch 'release/v1.8' into fix/AG-18132

commit 481ed62
Author: Stanislav A <s.atroschenko@adguard.com>
Date:   Fri Dec 16 21:57:14 2022 +0300

    add comment

commit dc38b52
Author: Stanislav A <s.atroschenko@adguard.com>
Date:   Thu Dec 15 21:41:26 2022 +0300

    refactor and update readme

commit 35440f5
Author: Stanislav A <s.atroschenko@adguard.com>
Date:   Thu Dec 15 19:53:30 2022 +0300

    Handle getScriptletFunction calls on unknown scriptlet names

README.md

@@ -161,9 +161,10 @@ And also there is a module at `dist/scriptlets.js` which has been exported to a
 
 ```javascript
 /**
- * Returns scriptlet code
+ * Returns scriptlet code by param
  * @param {Source} source
- * @returns {string}
+ * @returns {string|null} scriptlet code
+ * @throws on unknown scriptlet name
  */
 scriptlets.invoke(source);
 ```

src/scriptlets/index.js

@@ -29,16 +29,24 @@ import { getScriptletFunction } from '../../tmp/scriptlets-func';
  * Returns scriptlet code by param
  * @param {Source} source
  * @returns {string|null} scriptlet code
+ * @throws on unknown scriptlet name
  */
 function getScriptletCode(source) {
     if (!validator.isValidScriptletName(source.name)) {
         return null;
     }
 
-    const scriptletFunction = getScriptletFunction(source.name).toString();
+    const scriptletFunction = getScriptletFunction(source.name);
+    // In case isValidScriptletName check will pass invalid scriptlet name,
+    // for example when there is a bad alias
+    if (typeof scriptletFunction !== 'function') {
+        throw new Error(`Error: cannot invoke scriptlet with name: '${source.name}'`);
+    }
+    const scriptletFunctionString = scriptletFunction.toString();
+
     const result = source.engine === 'corelibs' || source.engine === 'test'
-        ? wrapInNonameFunc(scriptletFunction)
-        : passSourceAndProps(source, scriptletFunction);
+        ? wrapInNonameFunc(scriptletFunctionString)
+        : passSourceAndProps(source, scriptletFunctionString);
     return result;
 }