Crashes on decoding partial YAML

[kkebo]

How to reproduce:

let obj = try UniYAML.decode("a: ")

Expected result:

obj == nil

Actual result:

It crashes.

ID:           F499B549-9FB7-45AC-A277-B33766C91B89
Process:      DevToys [12392]
Identifier:   DevToys
Date/Time:    2023-05-05 05:53:23 +0000

Application Specific Information:
dyld: dyld config: DYLD_INSERT_LIBRARIES=/System/Library/PrivateFrameworks/PreviewsInjection.framework/PreviewsInjection
libswiftCore.dylib: Swift/StringIndexValidation.swift:121: Fatal error: String index is out of bounds

Thread:
0      libswiftCore.dylib                               closure #1 in closure #1 in closure #1 in _assertionFailure(_:_:file:line:flags:)
1      libswiftCore.dylib                               closure #1 in closure #1 in _assertionFailure(_:_:file:line:flags:)
2      libswiftCore.dylib                               _assertionFailure(_:_:file:line:flags:)
3      libswiftCore.dylib                               _StringGuts.validateScalarIndex(_:)
4      libswiftCore.dylib                               String.subscript.getter
5      DevToys                                          static UniYAML.parseToken(_:index:to:honorDash:inFlow:) /var/mobile/Containers/Data/Application/8912EB0F-0FC1-48F3-A8F9-CA2C7872F283/Library/Caches/com.apple.Playgrounds/DerivedData/DevToys-hlchpxicvjmykxgvzllxejrkiuqt/SwiftPM/scratch/checkouts/swift-log/Sources/Logging/Logging.swift:544
6      DevToys                                          static UniYAML.decode(_:) /var/mobile/Containers/Data/Application/8912EB0F-0FC1-48F3-A8F9-CA2C7872F283/Library/Caches/com.apple.Playgrounds/DerivedData/DevToys-hlchpxicvjmykxgvzllxejrkiuqt/SwiftPM/scratch/checkouts/swift-log/Sources/Logging/Locks.swift:0