Fix parent points in unreachable code (#27400) (#27406)

In the binder, unreachable code mistakenly skips the `bindJSDoc` call in
`bindChildrenWorker`, which sets parent pointers. The fix is to call
`bindJSDoc` in the case of unreachable code as well.

src/compiler/binder.ts

@@ -640,6 +640,7 @@ namespace ts {
         function bindChildrenWorker(node: Node): void {
             if (checkUnreachable(node)) {
                 bindEachChild(node);
+                bindJSDoc(node);
                 return;
             }
             switch (node.kind) {