Fix for __decorate emit on undecorated file following a decorated file

tests/cases/conformance/decorators/class/decoratedClassFromExternalModule.ts

@@ -0,0 +1,9 @@
+// @target: es6
+// @Filename: decorated.ts
+function decorate() { }
+
+@decorate
+export default class Decorated { }
+
+// @Filename: undecorated.ts
+import Decorated from 'decorated';