ICU crash on sorting when one codepoint is missing in collation

[KenZook]

Describe the bug

In Flex 9.0.8 (LT-20194) YurutiT project, Flex will crash when clicking the Choose Texts button. I discovered it was comparing "Yurutí Example Sentences" and "YURUTI KINSHIP TERMS" when it failed. The last i in the first word is NFD 69 301. This particular code point was not in the original collation rule

& i < ĩ <<< Ĩ << ĩ́ <<< Ĩ́

So I added it

& i < ĩ <<< Ĩ << í << ĩ́ <<< Ĩ́

and then the crash went away. So apparently ICU has some problem with this particular code point when it is not defined in the collation causing a crash. We are using an old ICU version. Perhaps the latest version would not have this crash. I would like to see us using a current version of ICU in Flex.

To Reproduce

Steps to reproduce the behavior:

1. Restore Yuruti
2. Go to Texts and Words
3. Click the Choose Texts button in toolbar.
   It crashes with a windows error. Event viewer has:
   Application: FieldWorks.exe
   Framework Version: v4.0.30319
   Description: The process was terminated due to an unhandled exception.
   Exception Info: System.AccessViolationException
   at Icu.NativeMethods.ucol_strcoll(SafeRuleBasedCollatorHandle, System.String, Int32, System.String, Int32)
   at Icu.Collation.RuleBasedCollator.Compare(System.String, System.String)
   at SIL.WritingSystems.IcuRulesCollator.Compare(System.String, System.String)
   at System.Collections.Generic.ArraySortHelper1[[System.__Canon, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]].InsertionSort(System._Canon[], Int32, Int32, System.Collections.Generic.IComparer1<System._Canon>)
   at System.Collections.Generic.ArraySortHelper1[[System.__Canon, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]].IntroSort(System._Canon[], Int32, Int32, Int32, System.Collections.Generic.IComparer1<System._Canon>)
   at System.Collections.Generic.ArraySortHelper1[[System.__Canon, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]].IntroSort(System._Canon[], Int32, Int32, Int32, System.Collections.Generic.IComparer1<System._Canon>)
   at System.Collections.Generic.ArraySortHelper1[[System.__Canon, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]].IntrospectiveSort(System._Canon[], Int32, Int32, System.Collections.Generic.IComparer1<System._Canon>)
   at System.Collections.Generic.ArraySortHelper1[[System.__Canon, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]].Sort(System._Canon[], Int32, Int32, System.Collections.Generic.IComparer1<System._Canon>)
   at System.Array.Sort[[System.__Canon, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]](System._Canon[], Int32, Int32, System.Collections.Generic.IComparer1<System._Canon>) at System.Collections.Generic.List1[[System.__Canon, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]].Sort(System.Comparison`1<System.__Canon>)
   at SIL.FieldWorks.IText.TextsTriStateTreeView.LoadTextsByGenreAndWithoutGenre()
   at SIL.FieldWorks.IText.TextsTriStateTreeView.LoadGeneralTexts()

(Ideally push a minimal solution that demonstrates the problem to https://gist.github.com)
Download YurutiT.zip from LT-20194.

Expected behavior

It should bring up the Choose Texts dialog

Screenshots

I was able to catch it in dnSpy 6.1.4.

Environment

• OS: Windows 8.1
• Exact version of icu.net 2.5.4+Branch.master.Sha.aa2e04611b4...
• .NET Framework/Core version ??

Additional context

This is very tricky to get it to fail. Sometimes it works, but usually not.