Update weapons.inc to fix zmarket buyzone bug

Using the original code:
    return bool:GetEntData(client, g_iToolsInBuyZone);
It is possible for clients to exploit zmarket by pressing the Rebuy button while pressing "W" to move forward. Changing to GetEntProp fixes buyzone detection for moving players. Not sure if this is wholly a CS:GO bug or not but it shouldn't break compatibility.