Add fallback for urls not conaining the "sp" tag

If ever YouTube changes thing again (or uses old urls for some unknown reason), this prevents the extractor from crashing.
As suggested here: https://github.com/TeamNewPipe/NewPipeExtractor/pull/163/files/133cc032d9987130927e4c00e78e9fdbca1331dd#r283529811

Author: Stypox

extractor/src/main/java/org/schabi/newpipe/extractor/services/youtube/extractors/YoutubeStreamExtractor.java

@@ -888,7 +888,13 @@ private Map<String, ItagItem> getItags(String encodedUrlMapKey, ItagItem.ItagTyp
                         String streamUrl = tags.get("url");
                         // if video has a signature: decrypt it and add it to the url
                         if (tags.get("s") != null) {
-                            streamUrl = streamUrl + "&" + tags.get("sp") + "=" + decryptSignature(tags.get("s"), decryptionCode);
+                            if (tags.get("sp") == null) {
+                                // fallback for urls not conaining the "sp" tag
+                                streamUrl = streamUrl + "&signature=" + decryptSignature(tags.get("s"), decryptionCode);
+                            }
+                            else {
+                                streamUrl = streamUrl + "&" + tags.get("sp") + "=" + decryptSignature(tags.get("s"), decryptionCode);
+                            }
                         }
                         urlAndItags.put(streamUrl, itagItem);
                     }