skip telnet authentication if username is empty

[BrianPugh]

Related: #171

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.89%. Comparing base (20068a9) to head (891c579).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #172   +/-   ##
=======================================
  Coverage   73.89%   73.89%           
=======================================
  Files          38       38           
  Lines        1632     1632           
  Branches      362      362           
=======================================
  Hits         1206     1206           
  Misses        338      338           
  Partials       88       88           

Flag	Coverage Δ
unittests	73.65% <ø> (ø)

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