graft: check for missing revision first before scanning working copy

Differential Revision: https://phab.mercurial-scm.org/D2753

mercurial/commands.py

@@ -2181,10 +2181,10 b' def _dograft(ui, repo, *revs, **opts):'
                 raise
             cmdutil.wrongtooltocontinue(repo, _('graft'))
     else:
+        if not revs:
+            raise error.Abort(_('no revisions specified'))
         cmdutil.checkunfinished(repo)
         cmdutil.bailifchanged(repo)
-        if not revs:
-            raise error.Abort(_('no revisions specified'))
         revs = scmutil.revrange(repo, revs)
 
     skipped = set()