updated caption file name and clean code

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

@@ -568,16 +568,16 @@ public class DownloadDialog extends DialogFragment
     private void onItemSelectedSetFileName() {
         final String setSubtitleLanguageCode = subtitleStreamsAdapter.getItem(selectedSubtitleIndex)
                 .getLanguageTag();
+        final String fileName = FilenameUtils.createFilename(getContext(),
+                currentInfo.getName());
         switch (dialogBinding.videoAudioGroup.getCheckedRadioButtonId()) {
             case R.id.audio_button:
             case R.id.video_button:
-                dialogBinding.fileName.setText(FilenameUtils.createFilename(getContext(),
-                        currentInfo.getName()));
+                dialogBinding.fileName.setText(fileName);
                 break;
             case R.id.subtitle_button:
-                dialogBinding.fileName.setText(FilenameUtils.createFilename(getContext(),
-                currentInfo.getName() + getString(
-                        R.string.caption_file_name, setSubtitleLanguageCode)));
+                dialogBinding.fileName.setText(fileName + getString(
+                        R.string.caption_file_name, fileName, setSubtitleLanguageCode));
                 break;
         }
     }

app/src/main/res/values/strings.xml

@@ -452,7 +452,7 @@
     <string name="resize_zoom">Zoom</string>
     <string name="caption_auto_generated">Auto-generated</string>
     <!-- Caption Settings -->
-    <string name="caption_file_name">-%s</string>
+    <string name="caption_file_name">%1$s-%2$s</string>
     <string name="caption_setting_title">Captions</string>
     <string name="caption_setting_description">Modify player caption text scale and background styles. Requires app restart to take effect</string>
     <!-- Debug Settings -->