Fix lineTo to do nothing instead of raising error when 0 length

[endikallanomatxin]

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Before the change it raised an error when startPoint and endPoint were equal

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 94.83%. Comparing base (33f72d2) to head (e3d6907).

Files	Patch %	Lines
cadquery/cq.py	0.00%	1 Missing and 1 partial :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1606      +/-   ##
==========================================
- Coverage   94.86%   94.83%   -0.04%     
==========================================
  Files          28       28              
  Lines        6231     6233       +2     
  Branches     1264     1265       +1     
==========================================
  Hits         5911     5911              
- Misses        193      194       +1     
- Partials      127      128       +1     

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[adam-urbanczyk]

Why is this desired? 0 length line sounds like a user mistake that should result in an error.

[endikallanomatxin]

When automating parametric design, it can be more comfortable not having to deal with the edge case of 0 length. At least in my case, it allowed for easier and more flexible parametric modelling. (A line that in some configurations has a finite length, can easily be omitted in other configurations when it is not needed)