tools/migrate: Prevent PTE truncation from being fatal duing the live phase

tools/migrate: Prevent PTE truncation from being fatal duing the live phase

It is possible, when normalising a PV pagetable that the table has been freed
and reused for something else by the guest.

In such a case, data read might no longer be a pagetable, and fail the
truncation check.  However, this should only be fatal if we encounter such a
page in the paused phase.

This check is now consistent with all other checks in the same area.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>