Shape of 'non_edge_index' in 'mol_building_env' causes invalid_losses > 0

[hohyun312]

gflownet/src/gflownet/envs/mol_building_env.py

Line 355 in f106cde

non_edge_index = np.zeros((2, 0), dtype=np.int64)

While running test tasks on 'mol_building_env', I encountered 'invalid_losses'. After investigating, I discovered that the shape of non_edge_index was incorrect. This issue can be easily fixed by setting non_edge_index = np.zeros((0, 2), dtype=np.int64). The correct shape is needed for line 382, where non_edge_index.shape[0] is used.