git: fix missing case from 6266d19556ad (introduction of nodeconstants)

Differential Revision: https://phab.mercurial-scm.org/D10241

hgext/git/gitlog.py

@@ -218,7 +218,7 b' class changelog(baselog):'
             n = nodeorrev
         # handle looking up nullid
         if n == nullid:
-            return hgchangelog._changelogrevision(extra={})
+            return hgchangelog._changelogrevision(extra={}, manifest=nullid)
         hn = gitutil.togitnode(n)
         # We've got a real commit!
         files = [