Use P_AproxDistance in old demos from older demoversions
As NeonSynth mentioned in #471 (closed) the old demos are broken in the prerelease of 2.2.9. This was due to more accurate functions used for calculating players' and enemies' speeds. This MR makes the game use old P_AproxDistance functions, only when viewing older demos, including title screen demos, reducing the desyncs.