[extractor/common] Improve base url construction

youtube_dl/extractor/common.py

@@ -1435,7 +1435,9 @@ class InfoExtractor(object):
                                 base_url = base_url_e.text + base_url
                                 if re.match(r'^https?://', base_url):
                                     break
-                        if not re.match(r'^https?://', base_url):
+                        if mpd_base_url and not re.match(r'^https?://', base_url):
+                            if not mpd_base_url.endswith('/') and not base_url.startswith('/'):
+                                mpd_base_url += '/'
                             base_url = mpd_base_url + base_url
                         representation_id = representation_attrib.get('id')
                         lang = representation_attrib.get('lang')