fix offscreen sprites sometimes being visible

_NOTICE

@@ -7,8 +7,6 @@ TODOs: (that i can remember right now)
 - settle on a network architecture
 - detect frames when Mario is in a controllable state
 - compute how many input neurons the network needs instead of hardcoding
-- rewrite positions to be relative to Mario
-'-> fix offscreen sprites sometimes being visible to network
 - add some detection for enemies later in the game
 - fix cfg.enable_overlay (smb.lua doesn't see it being changed)
 

smb.lua

@@ -88,9 +88,9 @@ local function set_timer(time)
 end
 
 local function mark_sprite(x, y, t)
-    if t == 0 then
+    if t == 0 or x <= -8 or x >= 0xFF or y <= 0 or y >= 0xE8 then
         -- place unused/unseen sprites
-        x = -0x08 -- just off the left side of the screen
+        x = -8 -- just off the left side of the screen
         y = 0xC8 -- at ground level.
     end