Avoid empty FRONTEND_VERSION with the new config style

When doing:

static:
  cdn_assets_url: xxx

then FRONTEND_VERSION would result to None & crash the homepage

Codecov Report

Merging #752 into master will not change coverage. The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master     #752   +/-   ##
=======================================
  Coverage   85.91%   85.91%           
=======================================
  Files         197      197           
  Lines       13207    13207           
=======================================
  Hits        11347    11347           
  Misses       1860     1860           

Impacted Files	Coverage Δ
arkindex/project/settings.py	0.00% <0.00%> (ø)

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added 7 commits

• 7fd37b92...059083f8 - 6 commits from branch master
• 0559093c - Avoid empty FRONTEND_VERSION with the new config style

Compare with previous version

enabled an automatic merge when the pipeline for 0559093c succeeds

canceled the automatic merge

mentioned in commit 1d153f1a

merged