memory: keep the owner of the AddressSpace alive until do_address_space_destroy This fixes a use-after-free if do_address_space_destroy is executed too late. Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com> Tested-by: Michael Roth <mdroth@linux.vnet.ibm.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>