Core/Loot: Fix master loot

Players will be able to open the loot window and see the items in case of master loot.
If the item is under threshold FFA applies, else the item becomes locked. If you try to loot "You don't meet the requirements to loot that item" notification appears. 
Also fix an exploit related to master loot item give.

This fix is based on a youtube video, if you have retail experience please confirm the correctness.