[SoundCloud] Return empty video stream list instead of null

Also replace every instance of `return new ArrayList<>();` with `return Collections.emptyList();`

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

@@ -277,8 +277,8 @@ public class MediaCCCStreamExtractor extends StreamExtractor {
 
     @Nonnull
     @Override
-    public List<String> getTags() {
+    public List<String> getTags() throws ParsingException {
-        return new ArrayList<>();
+        return Collections.emptyList();
     }
 
     @Nonnull

extractor/src/main/java/org/schabi/newpipe/extractor/services/soundcloud/extractors/SoundcloudStreamExtractor.java

@@ -235,12 +235,12 @@ public class SoundcloudStreamExtractor extends StreamExtractor {
 
     @Override
     public List<VideoStream> getVideoStreams() throws IOException, ExtractionException {
-        return null;
+        return Collections.emptyList();
     }
 
     @Override
     public List<VideoStream> getVideoOnlyStreams() throws IOException, ExtractionException {
-        return null;
+        return Collections.emptyList();
     }
 
     @Override
@@ -304,7 +304,7 @@ public class SoundcloudStreamExtractor extends StreamExtractor {
     @Nonnull
     @Override
     public List<String> getTags() throws ParsingException {
-        return new ArrayList<>();
+        return Collections.emptyList();
     }
 
     @Nonnull

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

@@ -1087,7 +1087,7 @@ public class YoutubeStreamExtractor extends StreamExtractor {
     @Nonnull
     @Override
     public List<String> getTags() {
-        return new ArrayList<>();
+        return Collections.emptyList();
     }
 
     @Nonnull