Display subtitles after seeking when paused

### Issue description
Subtitles won't appear if video is paused during seeking, in `SimpleExoPlayerView.ComponentListener.onCues(List cues)` we won't get any subtitles until we continue to play the video

### Reproduction steps
**1**. find some project (e.g. ExoPlayer demo).
**2**. add mediasource to play some video with subtitles
```
MediaSource videoAndSubtitles = new MergingMediaSource(videoMediaSource, textMediaSource);
exo.prepare(videoAndSubtitles);
exo.setPlayWhenReady(true);
```
**3**. it will start playing video and showing subtitles ok
**4**. pause video (use ExoPlayer demo control view buttons to pause/play video)
**5**. while video (playback) is paused try to seek though video (use ExoPlayer demo control SeekBar to change playback time)
**6**. you will never see subtitles
**7**. so subtitles will only appear if you continue playing video (press play button), but won't appear if video (playback) is paused
**8**. reason in `onCues(List cues)` we always get empty list (size 0) https://github.com/google/ExoPlayer/blob/release-v2/library/ui/src/main/java/com/google/android/exoplayer2/ui/SimpleExoPlayerView.java#L869

### Version of ExoPlayer being used
r2.5.2

### Device(s) and version(s) of Android being used
6.01 (23), Xiaomi Redmi 4 Pro/Prime