[Refactor] skip getProto call when AsyncFunction does not exist

Author: ljharb

index.js

@@ -43,5 +43,5 @@ module.exports = function isAsyncFunction(fn) {
 // eslint-disable-next-line no-extra-parens
 AsyncFunction = asyncFunc ? /** @type {import('.').AsyncFunction} */ (getProto(asyncFunc)) : false;
 }
-return getProto(fn) === AsyncFunction;
+return AsyncFunction && getProto(fn) === AsyncFunction;
 };