Fix offset of faces with holes

[jdegenstein]

Currently, offset of faces with holes can fail when the length of the inner wires reaches zero. This causes confusion for users especially with offsets of text that frequently contains holes.

This PR fixes that issue by silently deleting the inner wires if there is an exception while offsetting them. This example now works properly:

with BuildSketch() as s:
    t = Text("build", 20)
    offset(amount=5, mode=Mode.ADD)

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (61a3610) 96.00% compared to head (9919882) 96.01%.

❗ Current head 9919882 differs from pull request most recent head 911e120. Consider uploading reports for the commit 911e120 to get more accurate results

Files	Patch %	Lines
src/build123d/operations_generic.py	57.14%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #491      +/-   ##
==========================================
+ Coverage   96.00%   96.01%   +0.01%     
==========================================
  Files          24       24              
  Lines        7458     7461       +3     
==========================================
+ Hits         7160     7164       +4     
+ Misses        298      297       -1     

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