Return no search results when there are no readable corpora

Codecov Report

Merging #650 into master will increase coverage by 0.01%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #650      +/-   ##
==========================================
+ Coverage   86.14%   86.16%   +0.01%     
==========================================
  Files         181      181              
  Lines       13273    13290      +17     
==========================================
+ Hits        11434    11451      +17     
  Misses       1839     1839

Impacted Files	Coverage Δ
arkindex/project/mixins.py	84.61% <100%> (+0.61%)
arkindex/documents/tests/test_search_api.py	100% <100%> (ø)

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added 7 commits

• d5c0fb23...ff4a1647 - 6 commits from branch master
• a5a95cf1 - Return no search results when there are no readable corpora

Compare with previous version

mentioned in commit bdb35931

merged