Fix Projects::Ml::CandidatesController#show - undefined method can?' for nil:NilClass (ActionView::Template::Error)`

What does this MR do and why?

Fix sentry error for anonymous users on Projects::Ml::CandidatesController#show - undefined method can?' for nil:NilClass (ActionView::Template::Error)`

Related to #513099 (closed)

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Screenshots or screen recordings

How to set up and validate locally

1. Go to any project, and "Analyze/Experiments.
2. First create some experiments and runs as below on rails console

project = Project.find(34)
user = User.find_by_username('test4')

Ml::CreateModelService.new(project, "model_1", user).execute
m = ::Ml::Model.find_by(name: "model_1")
12.times { |i| Ml::CreateCandidateService.new(m.default_experiment, {user: user}).execute }


#  Add some ci info here
ca = Ml::Candidate.last
ca.update  ci_build:  Ci::Build.last

3. You should assign a ci_build_id to some candidate.

Then navigate to the run as an anonymous user in browser's incognito mode for example