fix(ngTouch): update workaround for desktop Webkit quirk

Fix click busting of input click triggered by a label click quickly
following a touch event on a different element, in desktop
and mobile WebKit

To reproduce the issue fixed by this commit set up a page with
 - an element with ng-click
 - a radio button (with hg-model) and associated label
In a quick sequence tap on the element and then on the label.
The radio button will not be checked, unless PREVENT_DURATION has passed

Fixes #6302