Follow on from CVE-2014-3571. This fixes the code that was the original source

of the crash due to p being NULL. Steve's fix prevents this situation from
occuring - however this is by no means obvious by looking at the code for
dtls1_get_record. This fix just makes things look a bit more sane.

Conflicts:
	ssl/d1_pkt.c

Reviewed-by: Dr Stephen Henson <steve@openssl.org>