Don't emit "Disconnect" event if an error occurred

[jwodder]

Blocked by the need for zyansheep/rustyline-async#21 to be released.

To do:

• Update rustyline-async requirement for whatever version the above fix is released in
• Update THIRDPARTY.toml
• Update CHANGELOG

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (4010040) 82.78% compared to head (d7c27f6) 82.85%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #299      +/-   ##
==========================================
+ Coverage   82.78%   82.85%   +0.06%     
==========================================
  Files           8        8              
  Lines         761      764       +3     
==========================================
+ Hits          630      633       +3     
  Misses        131      131              

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