Remove early exit to allow marking as complete

The early exit allowed some jobs to fail to be marked as complete.

Changelog: fixed

lib/gitlab/background_migration/backfill_draft_status_on_merge_requests.rb

@@ -22,8 +22,6 @@ module Gitlab
       def perform(start_id, end_id)
         eligible_mrs = MergeRequest.eligible.where(id: start_id..end_id).pluck(:id)
 
-        return if eligible_mrs.empty?
-
         eligible_mrs.each_slice(10) do |slice|
           MergeRequest.where(id: slice).update_all(draft: true)
         end

spec/lib/gitlab/background_migration/backfill_draft_status_on_merge_requests_spec.rb

@@ -50,5 +50,19 @@ RSpec.describe Gitlab::BackgroundMigration::BackfillDraftStatusOnMergeRequests,
 
       subject.perform(mr_ids.first, mr_ids.last)
     end
+
+    it_behaves_like 'marks background migration job records' do
+      let!(:non_eligible_mrs) do
+        Array.new(2) do
+          create_merge_request(
+            title: "Not a d-r-a-f-t 1",
+            draft: false,
+            state_id: 1
+          )
+        end
+      end
+
+      let(:arguments) { [non_eligible_mrs.first.id, non_eligible_mrs.last.id] }
+    end
   end
 end