message: Don't call async write blocks with m_is_sending_notifications set
  It is unclear if this caused any immediate problems, but is a violation of the
  intended invariants.
diff: @@ -721,6 +721,7 @@ void Realm::run_writes()
  // It is safe to use a reference here. Elements are not invalidated by new insertions
  auto& write_desc = m_async_write_q.front();
  + {
  CountGuard sending_notifications(m_is_sending_notifications);
  try {
  m_coordinator->promote_to_write(*this);
  @@ -729,6 +730,7 @@ void Realm::run_writes()
  translate_schema_error();
  }
  cache_new_schema();
  + }
  // prevent any calls to commit/cancel during a simple notification
  m_notify_only = write_desc.notify_only;
  