[MediaCCC] Return empty list of video-only streams instead of null

extractor/src/main/java/org/schabi/newpipe/extractor/services/media_ccc/extractors/MediaCCCStreamExtractor.java

@@ -197,7 +197,7 @@ public class MediaCCCStreamExtractor extends StreamExtractor {
 
     @Override
     public List<VideoStream> getVideoOnlyStreams() {
-        return null;
+        return Collections.emptyList();
     }
 
     @Nonnull