rem: scheme_utf8_encode_to_buffer_len (string, nchars, NULL, 0, &ncodes);
add: scheme_utf8_encode_to_buffer_len (string, nchars, SCHEME_BYTE_STR_VAL(obj), SCHEME_BYTE_STRLEN_VAL(obj), &ncodes);
context: void updateSchemeByteStringFromBSTR (Scheme_Object * obj, BSTR bstr){  UINT len = SysStringLen (bstr);  long nchars;  mzchar * string = scheme_utf16_to_ucs4 (bstr, 0, len,					  NULL, 0,					  &nchars, 0);  if (nchars > SCHEME_BYTE_STRLEN_VAL(obj))      scheme_signal_error ("String updated with longer string");  long ncodes;  scheme_utf8_encode_to_buffer_len (string, nchars, NULL, 0, &ncodes);  SCHEME_BYTE_STRLEN_VAL(obj) = ncodes;}