CRASHFIX: changing spectated target lead to a crash if the new spectated player disconnected right after (closes #92)

block_league/src/arena_lib/arena_manager.lua

@@ -232,6 +232,7 @@ arena_lib.on_change_spectated_target("block_league", function(arena, sp_name, t_
 
     -- ritardo di 0.1 perché on_join non è ancora stato chiamato, quindi non hanno ancora la HUD
     minetest.after(0.1, function()
+      if not minetest.get_player_by_name(t_name) then return end
       for _, weap_name in pairs(block_league.get_player_weapons(t_name)) do
         block_league.HUD_weapons_update(arena, t_name, weap_name)
       end