Deal with implicitly UTF-16 decoded webpages

These webpages don't specify an encoding and rely on the BOM

youtube_dl/extractor/common.py

@@ -220,6 +220,8 @@ def _download_webpage_handle(self, url_or_request, video_id, note=None, errnote=
                           webpage_bytes[:1024])
             if m:
                 encoding = m.group(1).decode('ascii')
+            elif webpage_bytes.startswith(b'\xff\xfe'):
+                encoding = 'utf-16'
             else:
                 encoding = 'utf-8'
         if self._downloader.params.get('dump_intermediate_pages', False):