account_tx resume bugfix

This is a fix for RIPD-314. It's not a perfect fix, but it's a good temporary fix until the existing code can be improved.

This fix works by ensuring we get enough transactions to ensure we can find the marker transaction, even if the limit is small. A better fix would be to either encode the necessary number of transactions in the marker or to modify the query to always start from the marker transaction.
I actually felt this was clearer with the local variable.  Either way, do try to keep to 80 characters, pls!  :-)