Unify mbtowc() invocation and error handling
Unify mbtowc() invocation and error handling

An abstraction worth performing since we can unify the internal state
reset and there's currently no need to distinguish between the two
scenarios where mbtowc() returns -1 or 0.

DBOTW/pick,calleerlandsson/pick,calleerlandsson/pick,thoughtbot/pick,thoughtbot/pick,DBOTW/pick,DBOTW/pick,thoughtbot/pick,thoughtbot/pick,calleerlandsson/pick