in `where` operator, if `cond.ndim` is 1, there's no assertion for it's length == input/output.shape[0]

in src/top/tensor/transform.cc
line 1706 
```cpp
inline bool WhereShape(const cvm::NodeAttrs& attrs,
                       std::vector<TShape>* in_attrs,
                       std::vector<TShape>* out_attrs) {
```