[BUG] Errors for Dataset with No Categorical Columns

[tim5go]

For custom dataset with no categorical columns, the following error will raise when running python core_models/main.py ,

TypeError: reduce() of empty sequence with no initial value from https://github.com/sfme/RVAE_MixedTypes/blob/0555fc63b7f7cc5fa1910ffc19cd061b125dd54d/src/core_models/mixedDataset.py#L73-L75

I think adding a default 0 value in the reduce method should solve the problem.