Correctly shutdown in case we shut down the buffer

[mhanberg]

I believe this issue is from the genlsp process crashing and then being restarted by the supervisor and then the buffer restarting, which then starts to consume a stdio stream in the middle and you just can't recover from that.

We should probably think of the proper restart strategy for those processes, but its most likely that the app should just terminate if the expert process crashes.

Originally posted by @mhanberg in #366

[Draggu]

I will TAL at this