(check_composing_code): If the current composing

(check_composing_code): If the current composing
sequence doesn't end properly, return -1.
(DECODE_CHARACTER_ASCII): Update coding->composed_chars.
(DECODE_CHARACTER_DIMENSION1): Likewise.
(decode_coding_iso2022): Check validity of a composing sequence.
(code_convert_string): If the length of text to be converted is
shrunk to zero, don't perform code conversion.
(shrink_decoding_region): Fix previous change.