Convert a sequence of bytes encoded as UTF-8 to a Unicode character.
This function checks for incomplete characters, for invalid characters such as characters that are out of the range of Unicode, and for overlong encodings of valid characters.
Note that get_char_validated returns (gunichar)-2 if
max_len is positive and any of the bytes in the
first UTF-8 character sequence are nul.
the maximum number of bytes to read, or -1 if
a pointer to Unicode character encoded as UTF-8
the resulting character. If