If requested, actually treat uncomfirmed change as being uncomfirmed

This commit strengthens 1bbca249b202c4802cc2c4d4de4a26e6392b4d92 by updating the CWalletTx::IsConfirmed() function.

If (bSpendZeroConfChange==false), then IsConfirmed() should actually treat unconfirmed change as being unconfirmed.
Merge pull request #3657

fdbc2b1 If requested, actually treat uncomfirmed change as being uncomfirmed (b6393ce9-d324-4fe1-996b-acf82dbc3d53)