Make sure the size of the byte array we just dumped into the struct is big...

Make sure the size of the byte array we just dumped into the struct is big enough before calculating the targetInfo, otherwise we're accessing memory that doesn't belong to us

Fix out of bounds memory access https://build.kde.org/job/kio%20master%20kf5-qt5/PLATFORM=Linux,compiler=gcc/102/testReport/junit/%28root%29/TestSuite/kioslave_httpauthenticationtest/

Also remove a cast to quint32 that is not necessary since the member is already a quint32

Valgrind doesn't complain anymore.