changegroup: record changelogdone after fully consuming its data

Setting this as a side-effect of calling _close() is wonky. There's
only one group for changelog data. So we can wait until after all
data has been emitted before recording it.

Differential Revision: https://phab.mercurial-scm.org/D4136

mercurial/changegroup.py

@@ -607,7 +607,6 b' class cgpacker(object):'
         if self._nextclrevtolocalrev is not None:
             self._clrevtolocalrev = self._nextclrevtolocalrev
             self._nextclrevtolocalrev = None
-        self._changelogdone = True
 
         return closechunk()
 
@@ -730,6 +729,8 b' class cgpacker(object):'
 
         self._verbosenote(_('%8.i (changelog)\n') % size)
 
+        self._changelogdone = True
+
         clrevorder = clstate['clrevorder']
         mfs = clstate['mfs']
         changedfiles = clstate['changedfiles']