When removing "Ghost Items" from the inventory, the number may be negative or zero

While testing MC-9813 and trying to clear the ghost items from the inventory, the messages

2013-02-15 06:49:16 [CLIENT] [INFO] [CHAT] Inventar von Kumasasa geleert, -5 Gegenstände entfernt
2013-02-15 06:49:21 [CLIENT] [INFO] [CHAT] §cCould not clear the inventory of Kumasasa, no items to remove

were thrown (even there were all of the items removed)

Steps to reproduce:

• Clear the inventory
• Place a minecart in slot 1 of the hotbar
• Pick Block that item and place in empy slot (repeat some times)
• Switch to survival mode /gamemode 0.
• Place some minecarts
• Drop a minecart with Q
• Walk over it (Inventory will be filled)
• issue "/clear"