add new unit test for getScriptLexicalStructure

tests/cases/fourslash/scriptLexicalStructureItems2.ts

@@ -0,0 +1,12 @@
+/// <reference path="fourslash.ts"/>
+
+
+/////**/
+
+goTo.marker();
+edit.insertLine("module A");
+edit.insert("export class ");
+
+// should not crash
+verify.getScriptLexicalStructureListCount(1);
+