block writes while reading

Disabling writes during "wipe" and "first load" is not quite semantically what we want, it's writes during read we want to block. This happens because turning the music on or off tries to save the state, and it's easier to just ignore that persistence request than to rework the music code so it doesn't. "wipe" and "first load" are when we're actually reading (and enacting) state, but it's the act of reading rather than those two acts that should block writes.

It is also unwilling to write until it's done its first read, which I think is a feature; it makes it harder to accidentally blank out the player's data.

chameleonic.p8

@@ -1915,24 +1915,23 @@ function persist:init0()
  cartdata("ulimate_lizard_total_destruction_0_1")
  self.init0 = self.read
  self:read()
- self.ready=true
 end
 
 function persist:read()
+ self.ready=false
  local m = dget(0) == 0
  self.music = m
  if m then music_on() else music_off() end
  self.max_level = dget(1)
  self.recent_level = dget(2)
+ self.ready=true
 end
 
 function persist:wipe()
- self.ready=false
  for i=0,64 do
   dset(i,0)
  end
  self:read()
- self.ready=true
 end
 
 function persist:lvlstart()