fixed crash when mesh stash fails

src/otaconf/otaconf.be

@@ -176,6 +176,10 @@ otaconf.init = def (m)
     end
 
     def get_unregistered_devices(devices)
+      if devices == nil 
+        return []
+      end
+
       var registered_devices = persist.find('registered_devices')
       var unregistered_devices = []