QFile::seek() on character devices not working

There is a very subtle bug in the QFileDevice::seek() call.

Consider this if:

if (!d->fileEngine->seek(off) || !QIODevice::seek(off)) {

If d->fileEngine->seek succeeded there is no point to call QIODevice::seek. Most probably it should be changed into a:

if (!d->fileEngine->seek(off) && !QIODevice::seek(off)) {

This means if both failed then please bail out.