Extract Channel Avatar in related videos.

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

@@ -172,6 +172,11 @@ public class YoutubeStreamInfoItemExtractor implements StreamInfoItemExtractor {
                     .getObject(0).getString("url");
         }
 
+        if (videoInfo.has("channelThumbnail")) {
+            return JsonUtils.getArray(videoInfo, "channelThumbnail.thumbnails")
+                    .getObject(0).getString("url");
+        }
+
         return null;
     }