* wcsmbs/mbrtowc.c: Set flush to 1 for conversion function calls
depending on whether the input string is empty or not.
* wcsmbs/mbrtowc.c: Calling function without input means clearing the
given state and not avoiding this by modifying a local object.
* wcsmbs/wcrtomb.c: Likewise.
* iconv/skeleton.c: If no EMIT_SHIFT_TO_INIT is defined clear state
object since some incomplete characters might be in there.