Fix last batch size equals max batch size error

lib/gitlab/background_migration/prepare_untracked_uploads.rb

@@ -88,7 +88,7 @@ module Gitlab
           end
         end
 
-        yield(paths)
+        yield(paths) if paths.any?
       end
 
       def build_find_command(search_dir)

spec/lib/gitlab/background_migration/prepare_untracked_uploads_spec.rb

@@ -128,6 +128,18 @@ describe Gitlab::BackgroundMigration::PrepareUntrackedUploads, :sidekiq do
           expect(untracked_files_for_uploads.count).to eq(5)
         end
       end
+
+      context 'when the last batch size exactly matches the max batch size' do
+        it 'does not raise error' do
+          stub_const("#{described_class}::FIND_BATCH_SIZE", 5)
+
+          expect do
+            described_class.new.perform
+          end.not_to raise_error
+
+          expect(untracked_files_for_uploads.count).to eq(5)
+        end
+      end
     end
   end
 
@@ -216,6 +228,18 @@ describe Gitlab::BackgroundMigration::PrepareUntrackedUploads, :sidekiq do
           expect(untracked_files_for_uploads.count).to eq(5)
         end
       end
+
+      context 'when the last batch size exactly matches the max batch size' do
+        it 'does not raise error' do
+          stub_const("#{described_class}::FIND_BATCH_SIZE", 5)
+
+          expect do
+            described_class.new.perform
+          end.not_to raise_error
+
+          expect(untracked_files_for_uploads.count).to eq(5)
+        end
+      end
     end
   end