Report unmapped addresses in memory_dump (Jan Kiszka)

Instead of dumping incorrect (ie. previously read) data, report the
invalid virtual address to the user.

Signed-off-by: Jan Kiszka <jan.kiszka@web.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5023 c046a42c-6fe2-441c-8c8c-71466251a162
