The fix for CVE-2012-2110 did not take into account that the

'len' argument to BUF_MEM_grow and BUF_MEM_grow_clean is an
int in OpenSSL 0.9.8, making it still vulnerable. Fix by
rejecting negative len parameter.

Thanks to the many people who reported this bug and to Tomas Hoger
<thoger@redhat.com> for supplying the fix.