fixup

* [DownloadDialog.java] use *.opus extension instead of *.webm (bad change from 844f80a5f1)
* [StreamItemAdapter.java] show "opus" in format label instead of "WebM Opus"

app/src/main/java/org/schabi/newpipe/download/DownloadDialog.java

@@ -559,8 +559,16 @@ public class DownloadDialog extends DialogFragment implements RadioGroup.OnCheck
             case R.id.audio_button:
                 mainStorage = mainStorageAudio;
                 format = audioStreamsAdapter.getItem(selectedAudioIndex).getFormat();
-                mime = format.mimeType;
+                switch(format) {
-                filename += format.suffix;
+                    case WEBMA_OPUS:
+                        mime = "audio/ogg";
+                        filename += "opus";
+                        break;
+                    default:
+                        mime = format.mimeType;
+                        filename += format.suffix;
+                        break;
+                }
                 break;
             case R.id.video_button:
                 mainStorage = mainStorageVideo;

app/src/main/java/org/schabi/newpipe/util/StreamItemAdapter.java

@@ -140,7 +140,15 @@ public class StreamItemAdapter<T extends Stream, U extends Stream> extends BaseA
         if (stream instanceof SubtitlesStream) {
             formatNameView.setText(((SubtitlesStream) stream).getLanguageTag());
         } else {
-            formatNameView.setText(stream.getFormat().getName());
+            switch (stream.getFormat()) {
+                case WEBMA_OPUS:
+                    // noinspection AndroidLintSetTextI18n
+                    formatNameView.setText("opus");
+                    break;
+                default:
+                    formatNameView.setText(stream.getFormat().getName());
+                    break;
+            }
         }
 
         qualityView.setText(qualityString);