Editing txn in moderation sets expiration date and leads to premature point expirations.

Steps to reproduce:

Set "Transaction status" to "moderated".
Set "Expire points after" to "never".
Create a story to earn points.
Go into moderation queue and open "edit" transaction screen. (Notice that the "Expiration date" field is populated).
Save edited transaction.
Approve transaction.

Check userpoints_txn table (note that transaction row now has an expirydate and expired is set to 1)

Run cron.

Check userpoints_txn table (note that a new transaction row has been entered [operation = expiry] that nullifies earned points)