SSH-01-006: Add missing NULL check for ssh_packet_get_current_crypto()

Fixes T193

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>
(cherry picked from commit b55d7f3b73)

src/packet_crypt.c

@@ -103,6 +103,9 @@ int ssh_packet_decrypt(ssh_session session,
     }
 
     crypto = ssh_packet_get_current_crypto(session, SSH_DIRECTION_IN);
+    if (crypto == NULL) {
+        return SSH_ERROR;
+    }
     cipher = crypto->in_cipher;
 
     if (encrypted_size % cipher->blocksize != 0) {