Fix crash when surrogate pair handling multibyte Unicode characters

[pmachapman]

Fixes sillsdev/serval#822

---

This change is 

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.51%. Comparing base (7651a39) to head (f2dbc2c).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #361   +/-   ##
=======================================
  Coverage   72.51%   72.51%           
=======================================
  Files         423      423           
  Lines       35945    35945           
  Branches     4962     4962           
=======================================
  Hits        26066    26066           
  Misses       8781     8781           
  Partials     1098     1098           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Enkidu93]

Oops 😵 - thank you for fixing this, Peter. I'm surprised we didn't catch this earlier given that I totally flip-flopped things. Could you add a test to cover this?

@Enkidu93 reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @ddaspit)

[pmachapman]

Done - added a unit test which breaks on master with the crash.

Reviewable status: 1 of 2 files reviewed, all discussions resolved (waiting on @ddaspit)

[Enkidu93]

Perfect, thank you!

@Enkidu93 reviewed 1 of 1 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @ddaspit)

[Enkidu93]

I'm going to go ahead and merge this so it'll be included in the new Machine version.