Don't show preview if user has abandoned link
If the user dwells on a link for long enough, then the gateway makes a
request, which is allowed to complete regardless of whether or not the
response is required.
If the user abandons the link but the request completes before the
abandon completes - currently, ABANDON_END_DELAY is 300 ms - then the
preview will be rendered temporarily.
Fix this by not rendering the preview if the user has started to abandon