Update fakedata.py

[willfrey]

Raise an IndexError for FakeData.__getitem__() if the index would be out of range.

[codecov-io]

Codecov Report

Merging #780 into master will decrease coverage by 0.02%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master    #780      +/-   ##
=========================================
- Coverage   38.13%   38.1%   -0.03%     
=========================================
  Files          32      32              
  Lines        3126    3128       +2     
  Branches      487     488       +1     
=========================================
  Hits         1192    1192              
- Misses       1855    1857       +2     
  Partials       79      79

Impacted Files	Coverage Δ
torchvision/datasets/fakedata.py	22.85% <0%> (-1.39%)	⬇️

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[fmassa]

Thanks!