add test that would have highlighted #189

src/strass/strass_app/tests/test_sanitize_pdf.py

 import os
-from io import StringIO
+from io import BytesIO
+
+from pypdf import PdfWriter
 
 from strass_app import utils
 from strass_app.tests.test_base_test_case import TooledTestCase
@@ -21,3 +23,11 @@ class SafePDFTestCase(TooledTestCase):
         cv.seek(0)
         my_io = utils.safe_pdf(cv)
         self.check_no_js(my_io)
+
+    def test_binary_file_indirect_object_iter(self):
+        writer = PdfWriter()
+        writer.add_attachment("test.txt", b"content")
+        stream = BytesIO()
+        writer.write(stream)
+        my_io = utils.safe_pdf(stream)
+        self.check_no_js(my_io)