Fix LT-21867: Optional contexts don't work properly in Hermit Crab

[jtmaxwell3]

https://jira.sil.org/browse/LT-21867 reports that optional contexts don't work correctly. If a context is optional, then it should accept anything. But the code to traverse fsts doesn't accept the empty string. I wasn't able to fix the code to traverse fsts, so I changed the context code to check whether the context accepts the empty string.

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This change is 

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 85.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 70.47%. Comparing base (c5fa125) to head (1c1e7f1).

Files with missing lines	Patch %	Lines
src/SIL.Machine/FiniteState/Fst.cs	72.72%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #296   +/-   ##
=======================================
  Coverage   70.46%   70.47%           
=======================================
  Files         386      386           
  Lines       32256    32274   +18     
  Branches     4539     4542    +3     
=======================================
+ Hits        22729    22744   +15     
- Misses       8479     8481    +2     
- Partials     1048     1049    +1     

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[ddaspit]

This is definitely a bug in the Fst class. The class should properly handle the case where the start state is accepting. I would prefer that the Fst class is fixed. I took a stab at getting it to work in this PR. Let me know if it fixes the issue.

Reviewed 4 of 4 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @jtmaxwell3)

[jtmaxwell3]

Fixing the Fst class is a better solution, and it seems to work. Thanks! You can delete this pull request.

[Enkidu93]

Fixing the Fst class is a better solution, and it seems to work. Thanks! You can delete this pull request.

Fixed in the other PR.