Fix subtraction for decimals

[Xd-pro]

Currently the query looks like this:

"UPDATE " . $this->table . " SET amount = amount - ?, decimals = decimals - ? WHERE (xuid = ? OR username = ?) AND amount >= ? AND decimals >= ?"

Which will not allow subtracting decimals from a whole number balance. For example, if I had $10.00 and I wanted to take away $0.50, this query would fail because the decimals (00) is less than the amount of decimals I want to take (50).