Fix gate isset key (#1692)

* Check if key is set

* Use isset

* Fix

Author: barryvdh

src/DataCollector/GateCollector.php

@@ -64,7 +64,7 @@ public function addCheck($user, $ability, $result, $arguments = [])
         if (isset($arguments[0])) {
             if ($arguments[0] instanceof Model) {
                 $model = $arguments[0];
-                if ($model->getKeyName() && $model->hasAttribute($model->getKeyName())) {
+                if ($model->getKeyName() && isset($model[$model->getKeyName()])) {
                     $target = get_class($model) . '(' . $model->getKeyName() . '=' . $model->getKey() . ')';
                 } else {
                     $target = get_class($model);