When every player dies in network co-op, the host brings them back at
the last checkpoint without reverting. A revert restores the players'
all-dead flag from the saved game; this path left it set. With it set,
players_update_after_game neither respawns a player who dies nor ends
the game, so the next death, of one player or of all, left everyone
waiting for a respawn that never came. The flag is now cleared once a
player is back.
(cherry picked from commit 2e7c88b538b8aada54d0ce877740fb1be091e17d)
Milenko
d161df18ed