[migration] fix bug in `CWAttributeAddOp.revertprecommit_event`
The `rdefdef` attribute is set during the operation execution. In some the
operation crash before this assignment. In such case `revertprecommit` raise an
attribute error crashing the whole process and shadowing the original error.
This changeset detect and Avoid this situation.
<html>
<head>
<script type="text/javascript" src="../../data/jquery.js"></script>
<script src="../../data/cubicweb.js" type="text/javascript"></script>
<script src="../../data/cubicweb.compat.js" type="text/javascript"></script>
<script src="../../data/cubicweb.python.js" type="text/javascript"></script>
<script src="../../data/cubicweb.htmlhelpers.js" type="text/javascript"></script>
<script type="text/javascript" src="qunit.js"></script>
<link rel="stylesheet" type="text/css" media="all" href="qunit.css" />
<script src="cwmock.js" type="text/javascript"></script>
<script src="test_htmlhelpers.js" type="text/javascript"></script>
</head>
<body>
<div id="main">
</div>
<h1 id="qunit-header">cubicweb.htmlhelpers.js functions tests</h1>
<h2 id="qunit-banner"></h2>
<h2 id="qunit-userAgent"></h2>
<ol id="qunit-tests">
</body>
</html>