Fix load data function (#180)

Author: reluzita

src/aequitas/flow/datasets/generic.py

@@ -152,7 +152,7 @@ def _validate_splits(self) -> None:
     def load_data(self) -> None:
         """Load the dataset."""
         self.logger.info("Loading data.")
-        if hasattr(self, "data"):
+        if self._data is not None:
             return
         if self.extension == "parquet":
             read_method = pd.read_parquet