Fail to seek in buffered part without internet connection.

### Issue description
Im trying to seek in buffered part without internet connection.
Expected result: it is possible to start playback
Actual result: Exception

Video: [device-2020-05-22-130034.mp4.zip](https://github.com/google/ExoPlayer/files/4667340/device-2020-05-22-130034.mp4.zip)

Click listener for "2 SEC FORWARD":
`new OnClickListener() {
int initial = 4000;
@Override
public void onClick(View v) {
player.seekTo(0, initial);
initial += 2000;
}
}`

### Reproduction steps
Steps:
1) Open ExoPlayer demo app;
2) Start to play Widevine Dash: MP4, H264 -> WV: Clear SD(MP4, H264)
3) Pause immediately before playback will start;
4) Turn off internet connection
5) Seek to 4000
6) Seek to 6000

### Link to test content
WV: Clear SD (MP4,H264)
https://storage.googleapis.com/wvmedia/clear/h264/tears/tears_sd.mpd

### A full bug report captured from the device
I sent Bugreport to dev.exoplayer@gmail.com

### Version of ExoPlayer being used
2.11.4; Version from release-v2 branch;

### Device(s) and version(s) of Android being used
Xiaomi Mi A1 (Android 9)