changegroup: restore original behavior of _nextclrevtolocalrev 0548f696795b accidentally changed the behavior of cgpacker._close(). The old behavior moved _nextclrevtolocalrev to _clrevtolocalrev only when _nextclrevtolocalrev was present and then removed _nextclrevtolocalrev. The bad behavior performed this move then cleared _clrevtolocalrev because it was the same object as _nextclrevtolocalrev. This commit restores the previous behavior. Surprisingly, no tests changed as a result of this bad logic. I'm not sure why. Differential Revision: https://phab.mercurial-scm.org/D4155