Fixed crash problem

trainhud.lua

@@ -8,6 +8,9 @@ end)
 function advtrains.set_trainhud(name, text)
 	local hud = advtrains.hud[name]
 	local player=minetest.get_player_by_name(name)
+	if not player then
+	   return
+	end
 	if not hud then
 		hud = {}
 		advtrains.hud[name] = hud
@@ -53,4 +56,4 @@ function advtrains.hud_train_format(train, flip)
 	elseif vel>0 then
 		return firstLine.."\n"..secondLine.."\nPress up to accelerate, down to decelerate, sneak to stop."
 	end
-end
+end