Test for file upload util method

[maskaravivek]

Added test to increase coverage for isSelfOwned method.

[codecov-io]

Codecov Report

Merging #968 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #968      +/-   ##
=========================================
+ Coverage    6.86%   6.88%   +0.01%     
=========================================
  Files          99      99              
  Lines        5218    5218              
  Branches      484     484              
=========================================
+ Hits          358     359       +1     
+ Misses       4833    4832       -1     
  Partials       27      27

Impacted Files	Coverage Δ
...ain/java/fr/free/nrw/commons/upload/FileUtils.java	8.92% <0%> (+1.78%)	⬆️

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[whym]

Thanks!