qca-botan: fixed getting result size for ciphers
qca-botan: fixed getting result size for ciphers

Do not try to guess the result size. It rely with particular
algo and some other factors and so can be any. Just use
Pipe::remaining() for this purpose.

karolherbst/qca,oktavarium/qca,Bjoe/qca,sladage/qca,KDE/qca,Bjoe/qca,Bjoe/qca,Bjoe/qca,karolherbst/qca,highfidelity/qca,KDE/qca,highfidelity/qca,JoshuaKolden/qca,KDE/qca,oktavarium/qca,JoshuaKolden/qca,karolherbst/qca,JoshuaKolden/qca,karolherbst/qca,oktavarium/qca,sladage/qca,JoshuaKolden/qca,KDE/qca,sladage/qca,sladage/qca,oktavarium/qca,highfidelity/qca,highfidelity/qca