Polyseat 0.38.0

A game left running rendered flat out once nobody was watching. A seat caps
its games at the framerate the client asked for, and took that cap off again
when the client left. That was written on the belief that MangoHud reads its
file once, when a game starts, so that removing it would cost a running game
nothing. MangoHud rereads the file while the game runs. Somebody who
disconnected without quitting therefore left a game behind with no limit at
all, and since the seat also asks for a present mode that never blocks, nothing
else held it either: one game was found at 220 % of a core with no client, and
an OpenGL test program in a seat went from 60 to about 7000 frames a second
every time the cap was removed, and back every time it was written.

The cap now stays. A client arriving sets it to its own rate, as before, and a
game that was already running follows within seconds. Once the stream has
stayed gone, the daemon sets it to the rate of the seat's own mode, in the same
step that puts the mode back, where it used to remove it. Sunshine no longer
runs anything for the cap when a client leaves.

Measured in a seat with a Vulkan and an OpenGL program running throughout: the
cap removed and rewritten by the old script, then the same sequence with the
new one, where both stayed at 60 through every step that used to release them,
followed a 120 fps client up and came back to 60 for the seat's own mode.

Seats need provisioning again for this, recipe generation 66: the script and
Sunshine's configuration both change. Until a seat's Sunshine has been
restarted it still asks for the cap to be taken off, and the new script answers
that by leaving it alone.

Not measured: a real game through a real disconnect and reconnect on the
released build. The measurements above are from test programs, with the script
run by hand the way Sunshine and the daemon run it.