update app.py

app.py

@@ -82,7 +82,7 @@ def load_sample(index):
 
     image_filenames = []
     for i in range(4):
-        image_filenames[i] = f"thumbnails/image{index-1}_{i}.png"
+        image_filenames.append(f"thumbnails/image{index-1}_{i}.png")
 
     sample = torch.load(f"samples/val{index-1}.pt")
     #imgs = []