Export empty instead of 0 for seek position times

[barbeau]

In the MUSER app, we attempt to get the seek position of the song when an event is triggered. For example, the user taps on the screen Play button, and we generate a UI event for PLAY and a player event for PLAY when the song starts playing.

Depending on the state of player, the seek position may not be available at certain times. In that case, the function to get the position returns 0:
https://github.com/CUTR-at-USF/MUSER/blob/usf/app/src/main/java/com/simplecity/amp_library/utils/MusicServiceConnectionUtils.java#L99

For this reason, when we're exporting the data, we should leave the seek position blank/empty in the CSV file instead of outputting a 0 value.

[barbeau]

@kanch21 FYI, I've opened this issue so we can change how the data is exported for seek position. We should output empty data instead of 0 value to make it clearer that real seek position data wasn't available. We can talk next week about who implements this. cc @antcoder007