Fix gauges crash when player leaves less than 1 second after joining

mods/gauges/init.lua

@@ -44,6 +44,7 @@ minetest.register_entity("gauges:hp_bar", hp_bar)
 
 local function add_HP_gauge(name)
 	local player = minetest.get_player_by_name(name)
+	if player then
 		local pos = player:get_pos()
 		local ent = minetest.add_entity(pos, "gauges:hp_bar")
 		if ent ~= nil then
@@ -51,6 +52,7 @@ local function add_HP_gauge(name)
 			ent = ent:get_luaentity()
 			ent.wielder = player:get_player_name()
 		end
+	end
 end
 
 -- If health_bars not defined or set to true