Fix unassociated bot user

[shaydewael]

Summary

If a bot user has no association to a user id, make sure it's still defined.

Requirements (place an x in each [ ])

• 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.

[codecov]

Codecov Report

Merging #507 into master will increase coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #507      +/-   ##
=========================================
+ Coverage   85.26%   85.3%   +0.04%     
=========================================
  Files           6       6              
  Lines         346     347       +1     
  Branches       75      75              
=========================================
+ Hits          295     296       +1     
  Misses         29      29              
  Partials       22      22

Impacted Files	Coverage Δ
src/client.coffee	95% <100%> (+0.05%)	⬆️

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