Fixes #33001 (#33456)
Summary:
This fixes https://github.com/pytorch/pytorch/issues/33001.
When subtracting 1 from a empty array, instead of being `-1` as seems to be expected in the later code (while loop), because `size()` seems to be unsigned, it becomes a very large number. This causes a segfault during the while loop later in the code where it tries to access a empty array.
This issue seemed to happen only on the pi with the following example code: `v = torch.FloatTensor(1, 135).fill_(0); v[0, [1]] += 2`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33456
Differential Revision: D19963711
Pulled By: ezyang
fbshipit-source-id: 1dbddd59a5df544cd7e025fc540c9efe2c4e19f4
