Make sure that we always delegate the click event even if there is no
purchase link on the page currently. We then don't call attachToLinks
anymore, as we want to check whether we're in preview mode before
we call LaterPay's DialogManager.
Merge pull request #444 from laterpay/feature/fix-click-delegation-logic

Fix click delegation logic
Would be nice to have an associated issue! Anyway: lgtm, merging.