gnutls: out of bounds read in _gnutls_ciphertext2compressed (GNUTLS-SA-2013-2)

The gnutlsciphertext2compressed function in lib/gnutlscipher.c in GnuTLS 2.12.23 allows remote attackers to cause a denial of service buffer over-read and crash via a crafted padding length. NOTE: this might be due to an incorrect fix for CVE-2013-0169...