// was:moveToParent
private void MoveToParent()
{
Debug.Assert(HoldsMutex());
Debug.Assert(State == CursorState.VALID);
Debug.Assert(PageID > 0);
Debug.Assert(Pages[PageID] != null);
MemPage.assertParentIndex(Pages[PageID - 1], PagesIndexs[PageID - 1], Pages[PageID].ID);
Pages[PageID].releasePage();
PageID--;
Info.nSize = 0;
ValidNKey = false;
}