[frontend] fix call to stixCoreRelationshipsDistribution

[labo-flg]

If a country has a marking unavailable for a user, the dashboard query stixCoreRelationshipsDistribution crashes because said country is Restricted.

This is due to PR #6323.

Now the relationshipDistributions data are checked and returned with "Restricted" representative if the user cannot access one this side of the relationship. Before they were filtered out, leading to inconsistencies (see #6319).

The bug happens because we do a ...on Country { name } and name is non-nullable, but will be null because it's restricted.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.78%. Comparing base (b2aa068) to head (a35976a).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6580   +/-   ##
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  Coverage   67.78%   67.78%           
=======================================
  Files         532      532           
  Lines       65102    65102           
  Branches     5470     5471    +1     
=======================================
  Hits        44129    44129           
  Misses      20973    20973           

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