fix sanitize_fragment('\ufeff')

ox/html.py

@@ -440,7 +440,12 @@ def sanitize_fragment(html):
     if not html.strip():
         return html
     import lxml.html
+    try:
         body = lxml.html.document_fromstring(html).find('body')
+    except lxml.etree.ParserError as e:
+        if e.args and e.args[0] == 'Document is empty':
+            return html
+        raise e
     html = lxml.html.tostring(body, encoding='utf-8')[6:-7].decode('utf-8')
     if html.startswith('<p>') and html.endswith('</p>'):
         html = html[3:-4]