Guard against deleted project feature entry

In https://gitlab.com/gitlab-org/gitlab-ce/issues/66482, we see that a
project's `project_feature` association may be lazily loaded and hence
return `nil` if the entry is deleted if the `Project` is already loaded
in memory. To ensure we don't fail hard when this happens, assume all
features are disabled.

We can fix this issue by eager loading the `project_feature` in
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/32169, but we
shouldn't have to depend on that.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/66482

app/policies/project_policy.rb

@@ -502,6 +502,8 @@ class ProjectPolicy < BasePolicy
   end
 
   def feature_available?(feature)
+    return false unless project.project_feature
+
     case project.project_feature.access_level(feature)
     when ProjectFeature::DISABLED
       false

changelogs/unreleased/sh-guard-against-orphaned-project-feature.yml

+---
+title: Guard against deleted project feature entry in project permissions
+merge_request: 32187
+author:
+type: fixed

spec/policies/project_policy_spec.rb

@@ -94,6 +94,19 @@ describe ProjectPolicy do
     permissions.each { |p| is_expected.not_to be_allowed(p) }
   end
 
+  context 'with no project feature' do
+    subject { described_class.new(owner, project) }
+
+    before do
+      project.project_feature.destroy
+      project.reload
+    end
+
+    it 'returns false' do
+      is_expected.to be_disallowed(:read_build)
+    end
+  end
+
   it 'does not include the read_issue permission when the issue author is not a member of the private project' do
     project = create(:project, :private)
     issue   = create(:issue, project: project, author: create(:user))