Fix decryption of ciphertext created with 'header' => 'randomiv'

Patch originally from Paulo Andrade:
https://bugzilla.redhat.com/show_bug.cgi?id=2235322

The function sub key_and_iv () in the module Crypt/CBC/PBKDF.pm returns
two values: key and iv

In sub _read_key_and_iv in Crypt/CBC.pm, the key is set from the second
return value rather than the first, causing decryption failures (#6).

This commit changes sub _read_key_and_iv to use the first value instead,
fixing the problem.

Author: pghmcfc

lib/Crypt/CBC.pm

@@ -661,7 +661,7 @@ sub _read_key_and_iv {
 	croak "Ciphertext does not begin with a valid header for 'randomiv' header mode" unless defined $self->{iv};
 	croak "randomiv header mode cannot be used securely when decrypting with a >8 byte block cipher.\n"
 	    unless $self->blocksize == 8;
-	(undef,$self->{key}) = $self->pbkdf_obj->key_and_iv(undef,$self->{passphrase});
+	($self->{key},undef) = $self->pbkdf_obj->key_and_iv(undef,$self->{passphrase});
 	substr($$input_stream,0,16) = ''; # truncate
     }