Ignore out of range epic IDs

Including a Markdown reference with a large epic ID
(e.g. `&1161452270761535925900804973910297`) would cause an Error 500
with `ActiveModel::RangeError`. To fix this, we implement `reference_valid?`
for the `Epic` model.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/57367

ee/app/models/ee/epic.rb

@@ -107,6 +107,10 @@ module EE
         end
       end
 
+      def reference_valid?(reference)
+        reference.to_i > 0 && reference.to_i <= ::Gitlab::Database::MAX_INT_VALUE
+      end
+
       def link_reference_pattern
         %r{
           (?<url>

ee/spec/lib/banzai/filter/epic_reference_filter_spec.rb

@@ -69,6 +69,12 @@ describe Banzai::Filter::EpicReferenceFilter do
       expect(doc(text).to_s).to eq(ERB::Util.html_escape_once(text))
     end
 
+    it 'ignores out of range epic IDs' do
+      text = "Check &1161452270761535925900804973910297"
+
+      expect(doc(text).to_s).to eq(ERB::Util.html_escape_once(text))
+    end
+
     it 'does not process links containing epic numbers followed by text' do
       href = "#{reference}st"
       link = doc("<a href='#{href}'></a>").css('a').first.attr('href')