actiontable.js: Use event.currentTarget instead of the closest tr

This event is triggered due to delegation. If any onclick event is able
to bubble up this far that it gets triggered we can safely use whatever
it has been triggered for. (i.e. it can only be a tr[href])

refs #3298

public/js/icinga/behavior/actiontable.js

@@ -375,7 +375,7 @@
     ActionTable.prototype.onRowClicked = function (event) {
         var _this = event.data.self;
         var $target = $(event.target);
-        var $tr = $target.closest('tr');
+        var $tr = $(event.currentTarget);
         var table = new Selection($tr.closest('table.action, table.table-row-selectable')[0], _this.icinga);
 
         // some rows may contain form actions that trigger a different action, pass those through