Warning and error message assume the user always wants an ensemble

[cosmicnet]

Hello,

After setting ensemble_size=0 I received the following warning and error:

[WARNING] [2021-10-23 13:02:44,338:Client-autoPyTorch.automl_common.common.utils.backend] Directory /tmp/autoPyTorch_tmp_ac7d92b5-33f7-11ec-99e8-00155d03f9cc/.autoPyTorch/ensembles does not exist

[ERROR] [2021-10-23 13:02:44,338:Client-AutoPyTorch:ac7db48c-33f7-11ec-99e8-00155d03f9cc:1] No valid ensemble was created. Please check the logfile for errors. Default to the best individual estimator:[(1, 9, 50.0)]

When a user has specifically set the ensemble size to 0 I suggest that this warning and error should be suppressed.