Fix segfault with torch.orgqr. (#46700)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/41768
The fault was that a NULL `tau` would get passed to LAPACK function. This PR fixes that by checking whether the `tau` contains 0 elements at the beginning of the function.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46700
Reviewed By: albanD
Differential Revision: D24616427
Pulled By: mruberry
fbshipit-source-id: 92e8f1489b113c0ceeca6e54dea8b810a51a63c3
