test: check null proto-of-proto in util.inspect()

Add a test to check util.inspect()'s handling of a null
prototype-of-an-iterable-prototype. This covers a previously uncovered
code branch.

Refs: https://coverage.nodejs.org/coverage-0fd121e00c9d5987/lib/internal/util/inspect.js.html#L597

PR-URL: https://github.com/nodejs/node/pull/36399
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-util-inspect.js

@@ -3011,3 +3011,35 @@ assert.strictEqual(
       '}'
   );
 }
+
+{
+  // Confirm null prototype of generator prototype displays as expected.
+
+  function getProtoOfProto() {
+    return Object.getPrototypeOf(Object.getPrototypeOf(function* () {}));
+  }
+
+  function* generator() {}
+
+  const generatorPrototype = Object.getPrototypeOf(generator);
+  const originalProtoOfProto = Object.getPrototypeOf(generatorPrototype);
+  assert.strictEqual(getProtoOfProto(), originalProtoOfProto);
+  Object.setPrototypeOf(generatorPrototype, null);
+  assert.notStrictEqual(getProtoOfProto, originalProtoOfProto);
+
+  // This is the actual test. The other assertions in this block are about
+  // making sure the test is set up correctly and isn't polluting other tests.
+  assert.strictEqual(
+    util.inspect(generator, { showHidden: true }),
+    '[GeneratorFunction: generator] {\n' +
+    '  [length]: 0,\n' +
+    "  [name]: 'generator',\n" +
+    "  [prototype]: Object [Generator] { [Symbol(Symbol.toStringTag)]: 'Generator' },\n" + // eslint-disable-line max-len
+    "  [Symbol(Symbol.toStringTag)]: 'GeneratorFunction'\n" +
+    '}'
+  );
+
+  // Reset so we don't pollute other tests
+  Object.setPrototypeOf(generatorPrototype, originalProtoOfProto);
+  assert.strictEqual(getProtoOfProto(), originalProtoOfProto);
+}