return empty hash if unknow device

git-svn-id: https://redmine.imt-atlantique.fr/svn/xaal/code/Python/trunk@2149 b32b6428-25c9-4566-ad07-03861ab6144f

core/metadb/xaal/metadb/app.py

@@ -87,6 +87,7 @@ class MetaDB(object):
         dev = self.get_device(_device)
         if dev:
             return {'device':_device,'map' : dev}
+        return {'device':_device,'map' : {}}
         logger.info('Unknown device %s' % _device)
 
     def get_value(self,_device,_key):