Fixed SVD ignoring "some/full_matrices" flag for empty inputs

[IvanYashchuk]

For empty inputs torch.svd (and torch.linalg.svd) was returning incorrect results for some=True (full_matrices=False).
Behaviour on master branch:

In [1]: import torch
In [2]: a = torch.randn(0, 7)
In [3]: a.svd()
Out[3]: 
torch.return_types.svd(
U=tensor([], size=(0, 0)),
S=tensor([]),
V=tensor([[0., 0., 0., 0., 0., 0., 0.],
        [0., 0., 0., 0., 0., 0., 0.],
        [0., 0., 0., 0., 0., 0., 0.],
        [0., 0., 0., 0., 0., 0., 0.],
        [0., 0., 0., 0., 0., 0., 0.],
        [0., 0., 0., 0., 0., 0., 0.],
        [0., 0., 0., 0., 0., 0., 0.]]))
In [4]: a.svd(some=False)
Out[4]: 
torch.return_types.svd(
U=tensor([], size=(0, 0)),
S=tensor([]),
V=tensor([[0., 0., 0., 0., 0., 0., 0.],
        [0., 0., 0., 0., 0., 0., 0.],
        [0., 0., 0., 0., 0., 0., 0.],
        [0., 0., 0., 0., 0., 0., 0.],
        [0., 0., 0., 0., 0., 0., 0.],
        [0., 0., 0., 0., 0., 0., 0.],
        [0., 0., 0., 0., 0., 0., 0.]]))

some flag is ignored and 7x7 V matrix is returned in both cases. V should have 7x0 shape when some=True.

This PR fixes that.

[facebook-github-bot]

💊 CI failures summary and remediations

As of commit a877b8c (more details on the Dr. CI page):

---

💚 💚 Looks good so far! There are no failures yet. 💚 💚

---

This comment was automatically generated by Dr. CI (expand for details).

Follow this link to opt-out of these comments for your Pull Requests.

Please report bugs/suggestions to the (internal) Dr. CI Users group.

[codecov]

Codecov Report

Merging #51109 (a877b8c) into master (f7b339d) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master   #51109   +/-   ##
=======================================
  Coverage   80.91%   80.91%           
=======================================
  Files        1926     1926           
  Lines      210014   210013    -1     
=======================================
  Hits       169942   169942           
+ Misses      40072    40071    -1     

[mruberry]

Sorry for the delay in review, @IvanYashchuk. Thanks for the fix!

[facebook-github-bot]

@mruberry has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[facebook-github-bot]

@mruberry merged this pull request in 5e09ec6.