the buffer-flush function did not account for mbtowc returning 0
rather than 1 when converting the nul character. this prevented
advancing past it, instead repeatedly converting it into the output
wide character string until the max output length was exhausted.
if (s!=f->wbase && sw_write(f, f->wbase, f->wpos-f->wbase)==-1)
return -1;
while (c->l && l && (i=mbtowc(c->ws, (void *)s, l))>=0) {
if (s!=f->wbase && sw_write(f, f->wbase, f->wpos-f->wbase)==-1)
return -1;
while (c->l && l && (i=mbtowc(c->ws, (void *)s, l))>=0) {