Coop_Spawns state not loaded from demo footer during demo playback

[SirBofu]

If a demo is recorded with the -coop_spawns parameter, when played back, Woof must be run with the -coop_spawns parameter to play it back, or else a desync will occur if there are any multiplayer-only Things (particularly monsters). This occurs whether the demo is played back via the command-line prompt or embedded within a WAD itself. This may also happen with -solo_net.

In addition, if -coop_spawns is enabled when loading a WAD that has any multiplayer-only items in levels, demo desyncs will occur when the original demos did not have coop_spawns enabled.

(In DSDA-Doom, the demo will play back with -coop_spawns properly set based so long as the demo is loaded from the command line prompt, but it still has a bug where if the demo is loaded from a WAD file, it has the same buggy behavior.)

You will need a WAD that makes use of multiplayer-only enemies to recreate this reliably.

[rfomin]

We can't change the demo header because the demos would be incompatible with PrBoom+/DSDA/old Woof etc.

PrBoom+/DSDA also have a demo footer from which they can read command line paratmeters. We also have a demo footer, mostly for DSDA site scripts, but we ignore it when playing demos. It might be worth adding a demo footer reading.

[SirBofu]

Have adjusted issue title to reflect where the param is stored.