lexer: Always init line_ctr, for a more predictable interface, even if not needed

[erezsh]

Attempts to solve issue #1565

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.97%. Comparing base (f79772c) to head (f04ec75).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1567   +/-   ##
=======================================
  Coverage   89.97%   89.97%           
=======================================
  Files          52       52           
  Lines        8018     8019    +1     
=======================================
+ Hits         7214     7215    +1     
  Misses        804      804           

Flag	Coverage Δ
unittests	89.97% <100.00%> (+<0.01%)	⬆️

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