crashes if device runs out of space while streaming to disk

@tsheaff commented on [Wed Oct 26 2016](https://github.com/calm/ios/issues/1740)

![screen shot 2017-03-13 at 5 23 17 pm](https://cloud.githubusercontent.com/assets/1238684/23880582/c8056688-0811-11e7-8ec8-98737e1806ad.png)

Should wrap `writeData:` in a try-catch. Any better means of handling the catch than by simply swallowing?