Skip invalid outline nodes

[adrg]

Addresses #65

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This change is 

[codecov]

Codecov Report

Merging #101 into development will decrease coverage by 5.38%.
The diff coverage is 31.25%.

@@               Coverage Diff               @@
##           development     #101      +/-   ##
===============================================
- Coverage        62.32%   56.94%   -5.39%     
===============================================
  Files              154      154              
  Lines            28014    28029      +15     
===============================================
- Hits             17459    15960    -1499     
- Misses           10169    10185      +16     
- Partials           386     1884    +1498

Impacted Files	Coverage Δ
model/writer.go	75.07% <0%> (-5.56%)	⬇️
model/outlines.go	62.59% <100%> (-7.78%)	⬇️
model/reader.go	49.41% <28.57%> (-15.65%)	⬇️
internal/e2etest/utils.go	60% <0%> (-20%)	⬇️
ps/exec.go	62.96% <0%> (-18.52%)	⬇️
core/security/handlers.go	33.33% <0%> (-16.67%)	⬇️
model/optimize/image_ppi.go	59.7% <0%> (-16.42%)	⬇️
model/signature_handler.go	55.04% <0%> (-15.6%)	⬇️
ps/operations.go	53.45% <0%> (-13.68%)	⬇️
core/stream.go	31.08% <0%> (-13.52%)	⬇️
... and 99 more

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[gunnsth]

LGTM