fix: use_block_sparse_edges does not set to False when only 1 ProdN…

…odes in a ProdLayer

src/pyjuice/layer/prod_layer.py

@@ -29,8 +29,8 @@ def __init__(self, nodes: Sequence[ProdNodes], global_nid_start: Optional[int] =
         assert len(nodes) > 0, "No input node."
 
         use_block_sparse_edges = True
-        for nid in range(1, len(nodes)):
-            if nodes[0].group_size != nodes[nid].group_size or nodes[nid].is_sparse():
+        for nid in range(0, len(nodes)):
+            if nodes[nid].is_sparse() or nodes[0].group_size != nodes[nid].group_size:
                 use_block_sparse_edges = False
                 break
         self.use_block_sparse_edges = use_block_sparse_edges