Error is thrown if you run ":Semshi goto error" before opening a file

[CaerphillyMediaLtd]

Seems it's not handled, the following error occurs:

Error detected while processing function remote#define#CommandBootstrap[5]..remote#define#request:
line    2:
error caught in request handler '/home/levi/.vim/plugged/semshi/rplugin/python3/semshi:command:Semshi [['goto', 'error']]':
Traceback (most recent call last):
  File "/home/levi/.vim/plugged/semshi/rplugin/python3/semshi/plugin.py", line 119, in cmd_semshi
    func(self, *args[1:])
  File "/home/levi/.vim/plugged/semshi/rplugin/python3/semshi/plugin.py", line 163, in goto
    self._cur_handler.goto(*args, **kwargs)
AttributeError: 'NoneType' object has no attribute 'goto'

[numirias]

Thanks for reporting! An error should be thrown, but of course it should be expressive. I added a proper error message in #22.

(There's an unrelated issue I need to solve before being able to merge that.)