`stats` crashes if no repository has been read
$ ./reposurgeon
reposurgeon% stats
Traceback (most recent call last):
File "./reposurgeon", line 11203, in <module>
main()
File "./reposurgeon", line 11179, in main
interactive()
File "./reposurgeon", line 11168, in interactive
interpreter.cmdloop()
File "/nix/store/zrny7m8nmn9q9klrr32alyfkkf113wc8-python-2.7.10/lib/python2.7/cmd.py", line 142, in cmdloop
stop = self.onecmd(line)
File "./reposurgeon", line 7077, in onecmd
cmd.Cmd.onecmd(self, line)
File "/nix/store/zrny7m8nmn9q9klrr32alyfkkf113wc8-python-2.7.10/lib/python2.7/cmd.py", line 221, in onecmd
return func(arg)
File "./reposurgeon", line 8214, in do_stats
parse.line = self.chosen().name
AttributeError: 'NoneType' object has no attribute 'name'