Infinite Scroll: infinite-footer HTML at bottom of page when Infinite Scroll is not activated

[grdkly]

Steps to reproduce the issue

1. Create blog with only one post, e.g. fresh install of WP 4.6.1
2. Install Jetpack 4.3.1, enable Infinite Scroll with default settings.
3. Scroll to bottom of front page.

What I expected

Infinite Scroll is not activated.

What happened instead

Infinite Scroll HTML <div id="infinite-footer"> is included at bottom of page even though Infinite Scroll script and style have not been included.

Link to example

http://grdkly.com/wordpress/

Possible root cause

infinity.php: Testing is_last_batch() in function action_template_redirect() correctly prevents inclusion of Infinite Scroll script and style; a similar test is needed in function footer() to prevent inclusion of Infinite Scroll footer HTML <div id="infinite-footer">. The test was changed in #3553.