don't crash if the item list is empty

svn path=/trunk/KDE/kdebase/runtime/; revision=1190003

declarativeimports/core/datamodel.cpp

@@ -102,6 +102,7 @@ void DataModel::setItems(const QVariantList &list)
     //convert to vector, so data() will be O(1)
     m_items = list.toVector();
 
+    if (!list.isEmpty()) {
         int role = Qt::UserRole;
         m_roleNames.clear();
         foreach (QString roleName, list.first().value<QVariantMap>().keys()) {
@@ -109,6 +110,7 @@ void DataModel::setItems(const QVariantList &list)
             m_roleNames[role] = roleName.toLatin1();
         }
         setRoleNames(m_roleNames);
+    }
 
     //make the declarative view reload everything,
     //would be nice an incremental update but is not possible