Handle empty Path definition

[ruslansokolov]

Currently, a file with an empty Path (d="") will throw an error. I came across a file like that while generating SVGs using MathJax. Browsers and other tools seem to be render them fine.

Example (test.svg):

...<path id="MJX-1-TEX-N-2061" d=""></path>...

Before:

swiftdraw test.svg --format png --size 500x200 fails.

After:

swiftdraw test.svg --format png --size 500x200 succeeds.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.68%. Comparing base (335e287) to head (8f1df09).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #84   +/-   ##
=======================================
  Coverage   89.68%   89.68%           
=======================================
  Files         144      144           
  Lines       12122    12123    +1     
=======================================
+ Hits        10872    10873    +1     
  Misses       1250     1250           

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[swhitty]

Thank you 🙏🏻

I've added some tests and also covered paths that are just whitespace " "