[SoundCloud] Fix playlist next page generation

Author: Stypox

extractor/src/main/java/org/schabi/newpipe/extractor/services/soundcloud/SoundcloudPlaylistExtractor.java

@@ -145,7 +145,7 @@ private void computeInitialTracksAndNextIds() {
     }
 
     private void computeAnotherNextPageUrl() throws IOException, ExtractionException {
-        if (nextTrackIdsIndex >= nextTrackIds.size()) {
+        if (nextTrackIds == null || nextTrackIdsIndex >= nextTrackIds.size()) {
             nextPageUrl = ""; // there are no more tracks
             return;
         }
@@ -160,6 +160,7 @@ private void computeAnotherNextPageUrl() throws IOException, ExtractionException
             urlBuilder.append(","); // a , at the end is ok
         }
 
+        nextTrackIdsIndex = upperIndex;
         nextPageUrl = urlBuilder.toString();
     }
 

extractor/src/test/java/org/schabi/newpipe/extractor/services/soundcloud/SoundcloudPlaylistExtractorTest.java

@@ -7,10 +7,13 @@
 import org.schabi.newpipe.DownloaderTestImpl;
 import org.schabi.newpipe.extractor.ListExtractor;
 import org.schabi.newpipe.extractor.NewPipe;
+import org.schabi.newpipe.extractor.exceptions.ExtractionException;
 import org.schabi.newpipe.extractor.playlist.PlaylistExtractor;
 import org.schabi.newpipe.extractor.services.BasePlaylistExtractorTest;
 import org.schabi.newpipe.extractor.stream.StreamInfoItem;
 
+import java.io.IOException;
+
 import static org.junit.Assert.*;
 import static org.schabi.newpipe.extractor.ExtractorAsserts.assertIsSecureUrl;
 import static org.schabi.newpipe.extractor.ServiceList.SoundCloud;
@@ -70,7 +73,9 @@ public void testRelatedItems() throws Exception {
         }
 
         @Test
-        public void testMoreRelatedItems() {
+        public void testMoreRelatedItems() throws Exception {
+            defaultTestMoreItems(extractor);
+
             try {
                 defaultTestMoreItems(extractor);
             } catch (Throwable ignored) {