fix(59825): getNavigationTree crash on invalid class merge and function merge with expando members (#60152)

src/services/navigationBar.ts

@@ -760,6 +760,7 @@ function isSynthesized(node: Node) {
 // We want to merge own children like `I` in in `module A { interface I {} } module A { interface I {} }`
 // We don't want to merge unrelated children like `m` in `const o = { a: { m() {} }, b: { m() {} } };`
 function isOwnChild(n: Node, parent: NavigationBarNode): boolean {
+    if (n.parent === undefined) return false;
     const par = isModuleBlock(n.parent) ? n.parent.parent : n.parent;
     return par === parent.node || contains(parent.additionalNodes, par);
 }