Environment

Windows build number: [run "ver" at a command prompt]
Microsoft Windows [Version 10.0.18362.207]

Steps to reproduce

If a UTF-8 stream gets buffered in a loop, characters that consume more than one byte may get split at the buffer boundaries. Passing the buffer to WriteConsoleOutputCharacterA will corrupt the text because a conversion to UTF-16 is in place where these partials are treated as invalid UTF-8 characters and replaced with with U+FFFD characters.

Expected behavior

WriteConsoleOutputCharacterA should cache the partials and prepend them to the characters passed at the next call of this function, similar to the behavior of WriteConsoleA.

Actual behavior

UTF-8 partials result in corrupted text.
A discussion about this already began in #386 but was rather out of scope in this issue.