Fix race condition in task state table unref

crates/luaffi/src/lib.lua

@@ -8,16 +8,15 @@ local function __ref(value)
   if ref ~= nil and ref ~= 0 then
     __registry[FREELIST_REF] = __registry[ref]
   else
-    ref = #__registry + 1
+    ref = rawlen(__registry) + 1
   end
   __registry[ref] = value
   return ref
 end
 
 local function __unref(ref)
-  if ref < 0 then return nil end
-  local value = __registry[ref]
-  __registry[ref] = __registry[FREELIST_REF]
-  __registry[FREELIST_REF] = ref
-  return value
+  if ref > 0 then
+    __registry[ref] = __registry[FREELIST_REF]
+    __registry[FREELIST_REF] = ref
+  end
 end