DeviceRestHandler: test time_limit not negative
DeviceRestHandler: test time_limit not negative

Fixes: 59c8bd0cea1f ("DeviceRestHandler: new set of REST endpoints")
Signed-off-by: Jan Viktorin <3eab6ac54c005c4408f608556a6663b7f2abede7@fit.vutbr.cz>

BeeeOn/server,BeeeOn/server,BeeeOn/server,BeeeOn/server