Fix chunk block changes being sent out of order (#5169)

* Flush out all pending, buffered changes at the end of each tick, after every chunk is ticked. This makes every block update client-side in unison, instead of unlucky ones only being sent 1 tick later.
* Re-add buffer for outgoing network data; IOCP async WSASend has higher overhead than expected... Fixes regression introduced in 054a89dd9

src/ChunkMap.cpp

@@ -1339,10 +1339,18 @@ void cChunkMap::SpawnMobs(cMobSpawner & a_MobSpawner)
 void cChunkMap::Tick(std::chrono::milliseconds a_Dt)
 {
 	cCSLock Lock(m_CSChunks);
+
+	// Do the magic of updating the world:
 	for (auto & Chunk : m_Chunks)
 	{
 		Chunk.second.Tick(a_Dt);
 	}
+
+	// Finally, only after all chunks are ticked, tell the client about all aggregated changes:
+	for (auto & Chunk : m_Chunks)
+	{
+		Chunk.second.BroadcastPendingChanges();
+	}
 }