gh-121860: Fix crash when materializing managed dict (#121866)

The object's inline values may be marked invalid if the materialized
dict was already initialized and then deleted.

Lib/test/test_class.py

@@ -882,6 +882,24 @@ class TestInlineValues(unittest.TestCase):
         f.a = 3
         self.assertEqual(f.a, 3)
 
+    def test_rematerialize_object_dict(self):
+        # gh-121860: rematerializing an object's managed dictionary after it
+        # had been deleted caused a crash.
+        class Foo: pass
+        f = Foo()
+        f.__dict__["attr"] = 1
+        del f.__dict__
+
+        # Using a str subclass is a way to trigger the re-materialization
+        class StrSubclass(str): pass
+        self.assertFalse(hasattr(f, StrSubclass("attr")))
+
+        # Changing the __class__ also triggers the re-materialization
+        class Bar: pass
+        f.__class__ = Bar
+        self.assertIsInstance(f, Bar)
+        self.assertEqual(f.__dict__, {})
+
     def test_store_attr_type_cache(self):
         """Verifies that the type cache doesn't provide a value which  is
         inconsistent from the dict."""