When a transaction has no quote ref, render "@user wrote:" properly

Summary:
Fixes T12576. In Javascript, data.ref is null, which is getting turned into /quote/?ref=null.

The code already handles this case, just not with ref=null happening in JS:

https://secure.phabricator.com/source/phabricator/browse/master/src/applications/transactions/controller/PhabricatorApplicationTransactionCommentQuoteController.php;b54adc6161c205e146fabb801ca53a44d94da444$47-52

Test Plan:
{F4913862}

• Also quoted a normal comment on a normal object in a normal way.

Reviewers: amckinley, chad

Reviewed By: chad

Maniphest Tasks: T12576

Differential Revision: https://secure.phabricator.com/D17720