Recognise first run better when calling UpdateSchema

[jakeahumphreys]

Currently I've been lazy and just caught the exception thrown when we're in the situation where we've created the database file, but need to run a schema update to fill out the missing tables. It runs a query to get schema versions, but it can't run the query because the table doesn't exist. So right now I catch that exception, set CurrentVersion to null and do the update.

Ew.