log: cutoff at the max id past the cutoff_date

Previously we were using the min, which is always going to be equivalant
to the min id in the table.

data/model/log.py

@@ -162,7 +162,7 @@ def get_stale_logs_cutoff_id(cutoff_date):
   """ Gets the most recent ID created before the cutoff_date. """
   try:
     return (LogEntry
-            .select(fn.Min(LogEntry.id))
+            .select(fn.Max(LogEntry.id))
             .where(LogEntry.datetime <= cutoff_date)
             .tuples())[0][0]
   except IndexError: