Added dim check for index_copy_ (#21617)
Summary:
Fixing reported [bug](https://github.com/pytorch/pytorch/issues/20322)
The issue was related to not checking the dimensions of source vs destination tensors.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21617
Differential Revision: D15749963
Pulled By: izdeby
fbshipit-source-id: acff114c729fd9c0a9a51325e0ebd8b42e1f2fc1
