managed expired state inside the timer rather than just checking if the time has expired; makes sure the callback fires even for zero length timers

timer.lua

@@ -22,6 +22,7 @@ function timer:new(time, on_progress, on_finish)
 	self.timer = 0
 	self.on_progress = on_progress
 	self.on_finish = on_finish
+	self.has_expired = false
 	self:reset(time)
 end
 
@@ -30,7 +31,8 @@ function timer:update(dt)
 	if not self:expired() then
 		self.timer = self.timer + dt
 
-		--get the relevant callback
+		--set the expired state and get the relevant callback
+		self.has_expired = self.timer >= self.time
 		local cb = self:expired()
 			and self.on_finish
 			or self.on_progress
@@ -43,7 +45,7 @@ end
 
 --check if the timer has expired
 function timer:expired()
-	return self.timer >= self.time
+	return self.has_expired
 end
 
 --get the timer's progress from 0 to 1