Fix SobolEngine.fast_forward with n=0 (#5262)

[saitcakmak]

Summary:

A recent torch change made it so that n=0 is not a valid input to SobolEngine.fast_forward. This diff should fix the resulting failures (in internal CI).

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Differential Revision: D113989171

[meta-codesync]

@saitcakmak has exported this pull request. If you are a Meta employee, you can view the originating Diff in D113989171.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.59%. Comparing base (7abf5d6) to head (59f686b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5262   +/-   ##
=======================================
  Coverage   96.58%   96.59%           
=======================================
  Files         621      621           
  Lines       70744    70745    +1     
=======================================
+ Hits        68329    68335    +6     
+ Misses       2415     2410    -5     

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[meta-codesync]

This pull request has been merged in 00b03db.