text: Title: #354 fix causes IndexError: string index out of range
  Body: ## Classification:
  
  Bug
  
  ## Reproducibility:
  
  Just run this command through autokey.
  
  ``` python
  system.exec_command("fcitx-remote -s **fcitx-keyboard-us")
  ```
  
  ## Version
  
  AutoKey version: 0.95.10
  
  Used GUI (Gtk, Qt, or both): 
  
  If the problem is known to be present in more than one version, please list all of those.
  
  Installed via: (PPA, pip3, …). PPA
  
  Linux Distribution: Linux Mint 20
  
  ## Summary
  
  #354 adds some commands related to this problem. It causes the result.
  
  ## Expected Results
  
  Nothing happens.
  
  ## Actual Results
  
  ``` python
  Traceback (most recent call last):
    File "/usr/lib/python3/dist-packages/autokey/service.py", line 207, in __tryReleaseLock
      self.configManager.lock.release()
  RuntimeError: release unlocked lock
  2020-11-29 23:28:13,811 ERROR - service - Script error
  Traceback (most recent call last):
    File "/usr/lib/python3/dist-packages/autokey/service.py", line 485, in execute
      exec(script.code, scope)
    File "<string>", line 2, in <module>
    File "/usr/lib/python3/dist-packages/autokey/scripting.py", line 497, in exec_command
      if output[-1] == "\n":
  IndexError: string index out of range
  ```
  