Products.CMFActivity.SQLBase: Always commit before returning

Committing serves two purposes:
- obviously: it makes any transactional data change persistent
- less obviously: it releases the database transactional snapshot taken by
  any previously issued query, allowing that snapshot and all snapshots
  after it to be also freed (ex: garbage collecting the data records that
  no other transaction can see)
In the current state of the code flow, this does not change much: after
this method returns the code flow should quickly hit a commit anyway,
either in dequeueMessage or before handing control back to timerserver,
thereby ending the Zope-initiated transaction.
But this will not be true in a future version of the code.

product/CMFActivity/Activity/SQLBase.py

@@ -683,8 +683,8 @@ CREATE TABLE %s (
     while 1:
       result = self._getMessageList(db, **where_kw)
       if not result:
+        transaction.commit()
         return
-      transaction.commit()
       message_list = [Message.load(line.message, uid=line.uid, line=line)
                       for line in result]
       message_set = self._getExecutableMessageSet(activity_tool, db, message_list)
@@ -714,6 +714,7 @@ CREATE TABLE %s (
           self.assignMessageList(db, 0, distributable_uid_set)
           validated_count += distributable_count
           if validated_count >= MAX_VALIDATED_LIMIT:
+            transaction.commit()
             return
       line = result[-1]
       where_kw['above_priority_date_uid'] = (line.priority, line.date, line.uid)