Fix sketch hull failure due to overlapping geometries.

[huskier]

Resolved a ZeroDivisionError in the sketch hull algorithm that occurred when processing overlapping geometries.

Applying the fix will allow the code below to execute as intended.

import cadquery as cq
from cadquery.vis import show

sketch = (cq.Sketch()
          .push([(44,0)])
          .rect(40, 40)
          .reset()
          .push([(82, 0)])
          .circle(20)
          .reset()
          .hull())
		  
show(sketch)

[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.66%. Comparing base (0c0a661) to head (c26869e).
⚠️ Report is 21 commits behind head on master.

Files with missing lines	Patch %	Lines
cadquery/hull.py	25.00%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1889      +/-   ##
==========================================
- Coverage   95.74%   95.66%   -0.08%     
==========================================
  Files          29       29              
  Lines        7583     7591       +8     
  Branches     1141     1144       +3     
==========================================
+ Hits         7260     7262       +2     
- Misses        193      196       +3     
- Partials      130      133       +3     

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