[extractor/generic] Fix following incomplete redirects (#5640)

youtube_dl/extractor/generic.py

@@ -1453,7 +1453,7 @@ class GenericIE(InfoExtractor):
                 if refresh_header:
                     found = re.search(REDIRECT_REGEX, refresh_header)
             if found:
-                new_url = found.group(1)
+                new_url = compat_urlparse.urljoin(url, found.group(1))
                 self.report_following_redirect(new_url)
                 return {
                     '_type': 'url',