In the case of an error path, `cls` may be undefined on line 155 of core.py

[SimplicityGuy]

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've searched for any related issues and avoided creating a duplicate issue.

Description

When running using Python 3.6, I get the following error:

Traceback (most recent call last):
  File "/usr/local/bin/rtmbot", line 11, in <module>
    load_entry_point('rtmbot==0.4.0', 'console_scripts', 'rtmbot')()
  File "/usr/local/lib/python3.6/site-packages/rtmbot/bin/run_rtmbot.py", line 31, in main
    bot.start()
  File "/usr/local/lib/python3.6/site-packages/rtmbot/core.py", line 99, in start
    self._start()
  File "/usr/local/lib/python3.6/site-packages/rtmbot/core.py", line 74, in _start
    self.load_plugins()
  File "/usr/local/lib/python3.6/site-packages/rtmbot/core.py", line 155, in load_plugins
    plugin_config = self.config.get(cls.__name__, {})
UnboundLocalError: local variable 'cls' referenced before assignment

Reproducible in:

• This is reproducible in the sample project.
  RTMBot version: 0.4.0
  Python version: 3.6.0
  OS Version: Debian Stretch (running RTMBot in python:3.6 docker container)

Steps to reproduce:

1. docker run -it python:3.6 bash
2. pip install rtmbot
3. add a testing rtmbot.conf file
4. run rtmbot

Expected result:

I expected that the bot would run. (well, when real bot code was in the container...)

Actual result:

The following error happened:

root@2dc3d0e0a668:/# rtmbot
Traceback (most recent call last):
  File "/usr/local/bin/rtmbot", line 11, in <module>
    load_entry_point('rtmbot==0.4.0', 'console_scripts', 'rtmbot')()
  File "/usr/local/lib/python3.6/site-packages/rtmbot/bin/run_rtmbot.py", line 31, in main
    bot.start()
  File "/usr/local/lib/python3.6/site-packages/rtmbot/core.py", line 99, in start
    self._start()
  File "/usr/local/lib/python3.6/site-packages/rtmbot/core.py", line 74, in _start
    self.load_plugins()
  File "/usr/local/lib/python3.6/site-packages/rtmbot/core.py", line 155, in load_plugins
    plugin_config = self.config.get(cls.__name__, {})
UnboundLocalError: local variable 'cls' referenced before assignment

[SimplicityGuy]

There is a potential that cls is never defined in this code path. It's not specific to Python 3.6. Changing title.

[finnito]

I have run into this same issue @SimplicityGuy. This only occurs when I try specify a BASE_PATH in the rtmbot.conf file. Do you have this same configuration?

[BattleForged]

I have met the same issue in 0.4.1
Just because I write wrong plugin name in rtmbot.conf