fix child trade sequence to show nothing

This bug surfaced after the unit tests were written. The child trade
slot needs to show no item when the player does not have any item and
the happy mask shop is not open yet.

ootrando_overworldmap_hamsda/scripts/autotracking/auto_items.lua

@@ -192,6 +192,7 @@ local function updateChildTradeSequence(segment)
     if item then
         local value = ReadU8(segment, 0x8011A65B)
 
+        local VAL_NOTHING = 0xFF
         local VAL_EGG     = 0x21
         local VAL_CHICKEN = 0x22
         local VAL_LETTER  = 0x23
@@ -227,22 +228,26 @@ local function updateChildTradeSequence(segment)
 
         local newStage = 0
 
-        -- first, show egg or chicken if we haven't met zelda yet
+        -- first, show pre-mask shop states
 
+        -- always show nothing if we have it
+        if     value == VAL_NOTHING then newStage = 0 -- nothing
         -- always show egg if we have it
-        if     value == VAL_EGG then newStage = 1 -- egg
-        -- if we have chicken, show egg instead if talon hasn't woken yet
+        elseif value == VAL_EGG     then newStage = 1 -- egg
+        -- handle chicken cases
         elseif value == VAL_CHICKEN then
+            -- only show chicken if we already woke up talon
             if CHICKEN_SHOWN_TO_TALON then
                 autotracker_debug('showing chicken because talon isn\'t at the castle', DBG_DETAIL)
                 newStage = 2 -- chicken
+            -- show egg instead so that talon's check appears on the tracker
             else
                 autotracker_debug('showing egg instead of chicken because talon is at the castle', DBG_DETAIL)
                 newStage = 1 -- show egg so tracker shows talon's check
             end
 
-        -- now, override the actual held item with the one that represents your furthest progress
-        -- in the trade sequence
+        -- now that the mask shop is open, override the actual held item with the one that
+        -- represents your furthest progress in the trade sequence
 
         -- always show truth no matter what you're holding, relevant checks should appear accessible
         elseif EARNED_MASK_OF_TRUTH then newStage = 13