Prevent callback after close by sleeping before close

[philburk]

See #953

I could only reproduce this when using Bluetooth.

I then tried calling usleep(N*1000) before the stream is closed.
N. crashes:tries
10 => 0:10
5 => 0:10
1 => 1:10 in onDeviceUpdate()
no => 8:11

So it is a pretty tight race. It seems a short delay right before the close is enough to prevent the race. Five msec works OK but ten msec should be a safer value.

Add a sleep in the Oboe close method.

Originally posted by @philburk in #953 (comment)