Fix error with Navigable String doesn't have name

src/epub_converter/html_epub_preprocessor.py

@@ -132,7 +132,8 @@ def _remove_headings_content(content_tag, title_of_chapter: str):
             text = re.sub(r"[\s\xa0]", " ", text).lower()
             text = text.strip() # delete extra spaces
             if title_of_chapter == text or \
-                    (title_of_chapter in text and re.findall(r"^h[1-3]$", tag.name)):
+                    (title_of_chapter in text and
+                     re.findall(r"^h[1-3]$", tag.name or content_tag.name)):
                 _add_span_to_save_ids_for_links(tag, content_tag)
                 tag.extract()
             elif not isinstance(tag, NavigableString):