Fix message templates select order

I have newsletter "Test Newsletter" in database and custom templates:
`templates/newsletter/message/test-newsletter/message.html`,
`templates/newsletter/message/test-newsletter/message.txt`,
`templates/newsletter/message/test-newsletter/message_subject.txt`
in my project, but messages from "Test Newsletter" are send with default templates and not my custom ones.

Message template overrides for specific newsletters were never used,
because "global" message templates were always loaded first.

Fixed by changing the order in which templates are loaded.