What happen if show_http_message fails to reencode?

I'm trying to make my git server sends http messages in non-ASCII
encoding. And I have a question.

At 206-218 in remote-curl.c:

static int show_http_message(struct strbuf *type, struct strbuf *charset,
                 struct strbuf *msg)
{
    const char *p, *eol;

    /*
     * We only show text/plain parts, as other types are likely
     * to be ugly to look at on the user's terminal.
     */
    if (strcmp(type->buf, "text/plain"))
        return -1;
    if (charset->len)
        strbuf_reencode(msg, charset->buf, get_log_output_encoding());

What happen if the message has a character which cannot be encoded by
the encoding defined by i18n.logoutputencoding? Drops only the
character or brakes the whole message?

-EungJun