Edge case: upgrade/downgrade when repository doesn't exist

This change takes the case where repository doesn't exist on disk
and make it ignore but succeed the step, increasing or decreasing the
version depending on the operation.

app/services/projects/hashed_storage/base_repository_service.rb

@@ -38,7 +38,8 @@ module Projects
         # project was not originally empty.
         if !from_exists && !to_exists
           logger.warn "Can't find a repository on either source or target paths for #{project.full_path} (ID=#{project.id}) ..."
-          return false
+
+          return true
         elsif !from_exists
           # Repository have been moved already.
           return true

spec/services/projects/hashed_storage/migrate_repository_service_spec.rb

@@ -32,6 +32,16 @@ describe Projects::HashedStorage::MigrateRepositoryService do
       end
     end
 
+    context 'when repository doesnt exist on disk' do
+      let(:project) { create(:project, :legacy_storage) }
+
+      it 'skips the disk change but increase the version' do
+        service.execute
+
+        expect(project.hashed_storage?(:repository)).to be_truthy
+      end
+    end
+
     context 'when succeeds' do
       it 'renames project and wiki repositories' do
         service.execute

spec/services/projects/hashed_storage/rollback_repository_service_spec.rb

@@ -34,6 +34,16 @@ describe Projects::HashedStorage::RollbackRepositoryService, :clean_gitlab_redis
       end
     end
 
+    context 'when repository doesnt exist on disk' do
+      let(:project) { create(:project) }
+
+      it 'skips the disk change but decrease the version' do
+        service.execute
+
+        expect(project.legacy_storage?).to be_truthy
+      end
+    end
+
     context 'when succeeds' do
       it 'renames project and wiki repositories' do
         service.execute