graft: fix duplicate filter logic

mercurial/commands.py

@@ -2553,6 +2553,7 b' def graft(ui, repo, *revs, **opts):'
         n = ctx.extra().get('source')
         if n and n in repo:
             r = repo[n].rev()
+            if r in revs:
             ui.warn(_('skipping already grafted revision %s\n') % r)
             revs.remove(r)
     if not revs: