Fix deadlock when calling command within command_error handler

[andrewsayre]

Description:

Moves the invocation of the command_error callbacks outside of the held lock for commands so that other commands could be called within the callback.

Related issue (if applicable): fixes #58

Checklist:

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• Tests have been added/updated. No exclusions in .coveragerc permitted.
• README.MD updated (if necessary)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.68%. Comparing base (ea86b51) to head (6690861).

Additional details and impacted files

@@           Coverage Diff           @@
##              dev      #59   +/-   ##
=======================================
  Coverage   99.68%   99.68%           
=======================================
  Files          17       17           
  Lines        1604     1607    +3     
=======================================
+ Hits         1599     1602    +3     
  Misses          5        5           

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