Customize: Clicking on child elements of preview links fails to abort navigation to non-previewable links

[westonruter]

In Twenty Seventeen, the social links nav menu has SVG elements as children of the nav menu item links. The handleLinkClick function that handles delegated clicks on a elements is currently checking if the event.target lacks an href attribute and if so, it short-circuits since it's not a link. But if the user clicks on a child element, then the event.target is not actually the a element but the clicked element. The logic for getting the link element needs to change as follows:

- link = $( event.target );
+ link = $( event.target ).closest( 'a' );

[curdin]

Patch applies cleanly and works as expected. Latest Chrome and Safari macOS.

[westonruter]

In 39584:

Customize: Prevent navigation in preview when clicking on child elements of preview links that have non-previewable URLs.

Fixes #39098.

[westonruter]

Reopening for 4.7.1.

[dd32]

In 39585:

Customize: Prevent navigation in preview when clicking on child elements of preview links that have non-previewable URLs.

Props westonruter.
Merges [39584] to the 4.7 branch.
Fixes #39098.