Converts a string from UTF-8 to the encoding GLib uses for filenames.
Note that on Windows GLib uses UTF-8 for filenames; on other platforms, this function indirectly depends on the current locale.
The input string shall not contain nul characters even if the
len argument is positive. A nul character found inside the string
will result in error g_convert_error_illegal_sequence. If the filename encoding is not UTF-8 and the
conversion output contains a nul character, the error g_convert_error_embedded_nul is set and the function
a UTF-8 encoded string.
the length of the string, or -1 if the string is nul-terminated.
location to store the number of bytes in the input string that were successfully converted, or null.
Even if the conversion was successful, this may be less than
the number of bytes stored in the output buffer (not including the terminating nul).
The converted string, or null on an error.