Handle corner-case where no sensors are detected

[oliviertilmans]

In order to help detecting similar bug to the one that happened with Linux 3.15, I think something should be done when no sensors (or fans if for some reasons applesmc changes some day) are detected -- most likely, do nothing and report an error.

I am however not sure if killing the daemon if that's the case is the best thing to do, as for example with systemd it would respawn it automatically etc.

[dgraziotin]

I agree with this. The current approach is to log a message and exit(0). I am not even sure if I should use EXIT_FAILURE instead of EXIT_SUCCESS. Anyway, as I do not know which is the best thing to do, I will keep using this method to keep consistency