Update: handle invalid UTF-8 fragments

Update: handle invalid UTF-8 fragments

A 1-width UTF-8 character (that is not a valid ASCII character) is used to designate part of a complete UTF-8 character block (aka: 1-width UTF-8 characters are fragments).
Because this fragment cannot exist in isolation, it must be handled as either an invalid or an incomplete UTF-8 fragment.

Provide new status codes for handling incomplete UTF-8 fragments.
Update appropriate functions to detect and handle these invalid or incomplete fragments.