strncat and UTF-8

[Allin Cottrell <cottrell wfu edu>]

I'm wondering if there's a recommended GLib idiom for this task: 
copy at most n bytes from gchar *src to gchar *targ (both in UTF-8), 
ensuring that the material from src is "properly truncated" if need 
be. That is, one doesn't finish (before the final NUL) with a byte 
that fails to complete the UTF-8 representation of some character.

I can sort of see how this might be done (rather painfully) using 
the GLib Unicode Manipulation API but I wonder if anyone has a 
snappy implementation -- something like g_utf8_strncat(), if it were 
to exist.

Allin Cottrell