Make sure generated blocks have their timestamp set

behavior change: newly generated blocks are no longer momentarily activated.
this shouldn't matter for anyone and did not consistently apply to all blocks anyway

addresses issue from #15902 for new maps(!)

src/util/container.h

@@ -53,11 +53,16 @@ public:
 		return m_queue.front();
 	}
 
-	u32 size() const
+	size_t size() const
 	{
 		return m_queue.size();
 	}
 
+	bool empty() const
+	{
+		return m_queue.empty();
+	}
+
 private:
 	std::set<Value> m_set;
 	std::queue<Value> m_queue;