bugfix again for first init varaible

src/aiunn/finetune/trainer.py

@@ -202,6 +202,9 @@ class aiuNNTrainer:
 
     def finetune(self, output_path, epochs=10, lr=1e-4, patience=3, min_delta=0.001):
         """Finetune the upscaler model"""
+        
+        is_improved = False # first the model hasn't been improved
+        
         if self.data_loader is None:
             raise ValueError("Data not loaded. Call load_data first.")
         # setup logging