A stack index without the corresponding lua_State pointer is useless, because it
could reference another coroutine than the main thread and thus just assuming
globalconf.L is wrong. Fix this by also passing around the corresponding
lua_State pointer.
This improves the result for the following test:
coroutine.resume(coroutine.create(function()
drawin({}).visible = true
end))
Signed-off-by: Uli Schlachter <psychon@znc.in>