fix renderer removing packed tile data on swapped tiles

[greym0uth]

Fixes #559.

Problem

The render checks to see if the tile's old position and new position do not match and it greedily remove's it from the chunk at that old position. If a tile earlier in the iteration was placed at that tile's old location it will be removed and the tile data is lost.

Solution

We introduce a set and use it to check if the tile's old position in the chunk was updated by an entity in a previous iteration.