Fix mcl_shields is_blocking crash when object not found under player

mods/ITEMS/mcl_shields/init.lua

@@ -112,6 +112,7 @@ end
 
 function mcl_shields.is_blocking(obj)
 	if not obj:is_player() then return end
+        if mcl_shields.players[obj] then
 	local blocking = mcl_shields.players[obj].blocking
 	if blocking <= 0 then
 		return
@@ -123,6 +124,7 @@ function mcl_shields.is_blocking(obj)
 	end
 	return blocking, shieldstack
 end
+end
 
 mcl_damage.register_modifier(function(obj, damage, reason)
 	local type = reason.type