Bug Overspending wads at the HMS Bounty Hunter

[adeyke]

For the wad exchange at the HMS Bounty Hunter, if you enter a buy amount that's more than you can afford, it'll just keep going until you run out. However, after doing this, I noticed that the session result put the wads in the extreme negatives and my item_amount returned 0 for them, even though I actually had some left. My guess is that the amount is decremented by how much the request number of purchases would cost, even though the actual number of purchases ends up being lower.