Fix language switching using the undo tooltip

Introduced in I740600d18859422b2f98a5ef92d0321f6e9615a2.

We need to prevent the default action (navigating a link) so that
our custom code has a chance to run. Before it was synchronous so
it called location.href before default action had a chance to execute.
When it was made asynchronous, the default action got executed before
our custom code.

Change-Id: I292f99aa5f5ff536d8197174c317018462685866

resources/js/ext.uls.interface.js

@@ -192,6 +192,8 @@
 						dir: 'auto'
 					} )
 					.on( 'click', function ( event ) {
+						event.preventDefault();
+
 						// Track if event logging is enabled
 						mw.hook( 'mw.uls.language.revert' ).fire();