policy-endpoint-device: handle filters only if we have endpoints

Otherwise the filters are handled both in policy-node and here
and everything is messed up

Fixes: #536

src/scripts/policy-endpoint-device.lua

@@ -22,11 +22,14 @@ function rescan ()
     handleLinkable(si_ep)
   end
 
+  -- handle filters only if we have endpoints
+  if endpoints_om:get_n_objects () > 0 then
     for filter in streams_om:iterate {
       Constraint { "node.link-group", "+" },
     } do
       handleFilter(filter)
     end
+  end
 end
 
 function scheduleRescan ()