Issues in preprocessing.py (not 100% sure)

[hanghoo]

Hi @tkipf

In preprocessing.py (line 77~96), val_edges_false seems have chance to be in edges_all when I run multiple times. It will trigger assert ~ismember(val_edges_false, edges_all)

So, I guess the if condition may need to be modified.

By the way, some if ismember sentences are written twice (e.g., lines 71 to 74 and 83 to 95 in preprocessing.py). I am not sure if it is redundant.

Thank you very much!