Add ThreadNode update handler

core/thread-node.lua

@@ -21,7 +21,10 @@ function ThreadNode:checkUpdate()
       updateThread:start()
     end
 
-    self.state = love.thread.getChannel(self.threadChannel):pop() or self.state
+    local v = love.thread.getChannel(self.threadChannel):pop()
+    if v then
+      self:onUpdate(v)
+    end
   end
 end
 
@@ -30,4 +33,8 @@ function ThreadNode:afterExit()
   self:checkUpdate()
 end
 
+function ThreadNode:onUpdate(v)
+  self.state = v
+end
+
 return ThreadNode