annotate: start pager after we're sure we wont abort

This avoids needlessly putting a short error message into the pager.

mercurial/commands.py

@@ -361,7 +361,6 b' def annotate(ui, repo, *pats, **opts):'
 
     Returns 0 on success.
     """
-    ui.pager('annotate')
     if not pats:
         raise error.Abort(_('at least one filename or pattern is required'))
 
@@ -422,6 +421,8 b' def annotate(ui, repo, *pats, **opts):'
     if linenumber and (not opts.get('changeset')) and (not opts.get('number')):
         raise error.Abort(_('at least one of -n/-c is required for -l'))
 
+    ui.pager('annotate')
+
     if fm.isplain():
         def makefunc(get, fmt):
             return lambda x: fmt(get(x))