In order for this function to have any point, it has to be possible to
pass non-UTF-8 data to it, so annotate @str as being array-of-guint8
instead of utf8.
https://bugzilla.gnome.org/show_bug.cgi?id=672548
/**
* g_utf8_validate:
- * @str: a pointer to character data
+ * @str: (array length=max_len) (element-type guint8): a pointer to character data
* @max_len: max bytes to validate, or -1 to go until NUL
* @end: (allow-none) (out): return location for end of valid data
*