fix segfault in `cat` on CPU with tensors that can't be indexed with 32-bit ints. (#21530)
Summary:
Should be self-explanatory. This `int` variable is overflowing.
Reported in #21526
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21530
Differential Revision: D15719275
Pulled By: umanwizard
fbshipit-source-id: 24e917a00a5b78bc3af29ef3b8b72eea7e89d5d5
