Fix antique ghost netvars

Yesterday I opened issue #596 (closed) where I explained how some old replays had desynced ghosts that could potentially even crash the game when raced against. Turns out I was right with my guess that something was up with netvars. Since 2.2.7 netvars' names were saved in replays. Before that they were only presented by their UINT16 hash in the file.

The fix was to check the version the demo was made in, and choose the correct algorithm for skipping netvars. This should make the demos with netvars, made in 2.2.6 and before possible to race against.