Set minimum input for a transaction to 0.00000001 Dogecoin

The revision which removed input restrictions took the minimum input down to zero, resulting in vastly excessive calls to GetDebit() when sending money, as it did not correctly discount wallet entries with a value of zero.

This reverses that patch, but sets the minimum input to 0.00000001 Dogecoin. Sending 25 payments on a testnet node, this reduced calls to GetDebit from almost 1 million, down to slightly under 1,000.