src: delete BaseObjectWeakPtr data when pointee is gone

Fix the condition for deleting the underlying data pointed to by
a `BaseObjectWeakPtr`, which erroneously skipped that deletion
when `ptr->get()` was `nullptr`. This fixes a memory leak reported
by some of the tests.

Refs: #30374 (comment)

Backport-PR-URL: #32301
PR-URL: #32393
Reviewed-By: Matheus Marchini <mat@mmarchini.me>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

Author: addaleax

src/base_object-inl.h

@@ -230,13 +230,13 @@ BaseObject* BaseObjectPtrImpl<T, kIsWeak>::get_base_object() const {
 
 template <typename T, bool kIsWeak>
 BaseObjectPtrImpl<T, kIsWeak>::~BaseObjectPtrImpl() {
-  if (get() == nullptr) return;
   if (kIsWeak) {
-    if (--pointer_data()->weak_ptr_count == 0 &&
+    if (pointer_data() != nullptr &&
+        --pointer_data()->weak_ptr_count == 0 &&
         pointer_data()->self == nullptr) {
       delete pointer_data();
     }
-  } else {
+  } else if (get() != nullptr) {
     get()->decrease_refcount();
   }
 }