osc: set an arbitrary high Z-order

The main reason for this is just to make show the OSC always above
console.lua, instead of a random order.

(And this is also the only reason osc.lua was changed to the new API.
The old API could have been extended, but lets not.)

player/lua/osc.lua

@@ -137,6 +137,7 @@ function set_osd(res_x, res_y, text)
     state.osd.res_x = res_x
     state.osd.res_y = res_y
     state.osd.data = text
+    state.osd.z = 1000
     state.osd:update()
 end