dispatch: check for None before closing repo

We were trying to call close() if repo == None and req.repo != None.
This can happen when running commands that don't take a repo.

mercurial/dispatch.py

@@ -654,7 +654,7 b' def _dispatch(req):'
         return runcommand(lui, repo, cmd, fullargs, ui, options, d,
                           cmdpats, cmdoptions)
     finally:
-        if repo != req.repo:
+        if repo and repo != req.repo:
             repo.close()
 
 def _runcommand(ui, options, cmd, cmdfunc):