Fix Error 500 when referencing issue with project in pending delete

Closes #31215

app/models/issue.rb

@@ -199,7 +199,7 @@ class Issue < ActiveRecord::Base
   # Returns `true` if the current issue can be viewed by either a logged in User
   # or an anonymous user.
   def visible_to_user?(user = nil)
-    return false unless project.feature_available?(:issues, user)
+    return false unless project && project.feature_available?(:issues, user)
 
     user ? readable_by?(user) : publicly_visible?
   end

spec/lib/banzai/redactor_spec.rb

@@ -42,6 +42,19 @@ describe Banzai::Redactor do
       end
     end
 
+    context 'when project is in pending delete' do
+      it 'redacts an issue attached' do
+        project.pending_delete = true
+        project.save
+        issue = create(:issue, project: project)
+        redactor = described_class.new(project, user)
+        doc = Nokogiri::HTML.fragment("<a class='gfm' data-reference-type='issue' data-project=\"#{project.id}\" data-issue=\"#{issue.id}\">foo</a>")
+        redactor.redact([doc])
+
+        expect(doc.to_html).to eq('foo')
+      end
+    end
+
     context 'when reference visible to user' do
       it 'does not redact an array of documents' do
         doc1_html = '<a class="gfm" data-reference-type="issue">foo</a>'