Guard failed testItem creation

Summary: createObjectFromSource can return a null on error. This needs guarding.

Reviewers: #plasma, mart

Reviewed By: #plasma, mart

Subscribers: plasma-devel, #frameworks

Tags: #plasma, #frameworks

Differential Revision: https://phabricator.kde.org/D7532

src/plasmaquick/appletquickitem.cpp

@@ -676,8 +676,10 @@ QObject *AppletQuickItem::testItem()
         }
 
         d->testItem = d->qmlObject->createObjectFromSource(url, QtQml::qmlContext(rootItem()));
+        if (d->testItem) {
             d->testItem->setProperty("plasmoidItem", QVariant::fromValue<QObject*>(this));
         }
+    }
 
     return d->testItem;
 }