Core/Loot: Fix an exploit that allowed players to loot infinite amount of items that have condition(s)

You can loot *arbitrary* conditional item that is *unavailable* to the player, *infinite* times.

If the player doesn't meet the condition, the 'is_looted' field will be always false, and also a nice overflow happens:

Slot: 0 ItemID: 28558 Unlooted Count: 2 IsLooted: 0
Slot: 0 ItemID: 28558 Unlooted Count: 1 IsLooted: 0
Slot: 0 ItemID: 28558 Unlooted Count: 0 IsLooted: 0
Slot: 0 ItemID: 28558 Unlooted Count: 255 IsLooted: 0
Slot: 0 ItemID: 28558 Unlooted Count: 254 IsLooted: 0
Slot: 0 ItemID: 28558 Unlooted Count: 253 IsLooted: 0

How to reproduce?
For example kill Murmur (18708), make sure you don't have Blessing of Auchindoun (33377) aura and send CMSG_AUTOSTORE_LOOT_ITEM with slot = 0 (or use WPE). You can get as many Spirit Shard (28558) as you want.