Bug 30571: (follow-up) Additional check at upgrade

Bug 30571: (follow-up) Additional check at upgrade

Bad data occurs. We are removing null hosts here and update
empty syntax or encoding, informing the user.

Test plan:
Remove the NOT NULL condition if needed.
Copy db_revs/220600056.pl to atomicupdate and test dbrev.
You might see something like:
    Upgrade to 22.06.00.056  [11:48:22]: Bug 30571 - Table z3950servers: three cols NOT NULL
        Found bad data in table z3950servers: removed 1 records with host undefined
        Corrected empty syntax or encoding for the following hosts. Please check after upgrade.
        Updated hosts: lx2.loc.gov,lx2.loc.gov

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>