Makes sure `Mobify.ajs` is defined even for the v7 tag, which doesn't set the Mobify.ajs variable

Status: **Opened for visibility**

Reviewers: @tedtate @rrjamie 
JIRA: None

## Changes
- Makes sure Mobify.ajs is defined, even if the tag doesn't have it.

## How to test-drive this PR
- For a site that has a v7 tag, load a bundle and make sure Mobify.ajs is defined.