Fixed #2825 where user was able to add one lang twice

[madhurgupta10]

Description

Fixes #2825 The user should not be allowed to add the same language twice.

What changes did you make and why?

I added a check, where the first non selected language index will be picked instead of a static index.

Tests performed

Tested betaDebug on Xiaomi Mi A1 with API level 28.

[codecov-io]

Codecov Report

Merging #2834 into master will decrease coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master   #2834      +/-   ##
=========================================
- Coverage    3.43%   3.43%   -0.01%     
=========================================
  Files         246     246              
  Lines       12156   12166      +10     
  Branches     1064    1067       +3     
=========================================
  Hits          418     418              
- Misses      11707   11717      +10     
  Partials       31      31

Impacted Files	Coverage Δ
...r/free/nrw/commons/upload/DescriptionsAdapter.java	0% <0%> (ø)	⬆️
...ava/fr/free/nrw/commons/review/ReviewActivity.java	0% <0%> (ø)	⬆️

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[madhurgupta10]

@neslihanturan I have added comments :)

[neslihanturan]

Thanks works as intended for me @madhurgupta10