Don't fail when child gets no segments.

[Julian]

Closes #42.

[codecov-io]

Codecov Report

Merging #43 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #43      +/-   ##
==========================================
+ Coverage   97.72%   97.73%   +0.01%     
==========================================
  Files           6        6              
  Lines        1100     1105       +5     
  Branches      133      134       +1     
==========================================
+ Hits         1075     1080       +5     
  Misses         13       13              
  Partials       12       12

Impacted Files	Coverage Δ
hyperlink/test/test_url.py	99.79% <100%> (ø)	⬆️
hyperlink/_url.py	95.58% <100%> (+0.01%)	⬆️

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[mahmoud]

great work, done quick, perfect! thanks so much!