oat-decorate does not block when frame source is not present

[jonnew]

SHA: 4364184

To reproduce

~[0]$oat decorate raw dec -p pos &

~[0]$ oat posigen rand2D pos -r 5
posigen[*->pos]: Steaming to sink pos.
posigen[*->pos]: Press CTRL+C to exit.
pos completed write number: 0
pos completed write number: 1
pos completed write number: 
...

oat-posigen should be held up because raw is not being written to. 'posandrawwrites should be synchronized byoat-decoratebut they are not, andoat-posigen` spits positions to nowhere.