Don't attempt to save a new route on Geo secondary

The lazy initializer doesn't work on Geo for projects that have not
yet been visited. Geo would fail to sync projects that had this issue.

Closes #2743

app/models/concerns/routable.rb

@@ -144,6 +144,8 @@ module Routable
   end
 
   def update_route
+    return if Gitlab::Geo.secondary?
+
     prepare_route
     route.save
   end

spec/models/concerns/routable_spec.rb

@@ -12,6 +12,16 @@ describe Group, 'Routable' do
     it { is_expected.to have_many(:redirect_routes).dependent(:destroy) }
   end
 
+  describe 'Geo secondary' do
+    it 'does not save route if route is not present' do
+      group.route.path = ''
+      allow(Gitlab::Geo).to receive(:secondary?).and_return(true)
+      expect(group).to receive(:update_route).and_call_original
+
+      expect { group.full_path }.to change { Route.count }.by(0)
+    end
+  end
+
   describe 'Callbacks' do
     it 'creates route record on create' do
       expect(group.route.path).to eq(group.path)