wallet2: fix corner case failing to send a second output

If a rct transaction can be made with just one input, a second
output will be added. This output will be the smallest amount
output available. However, if this output is a non rct output
with less available fake outs than requested, the transaction
will be rejected. We now check the histogram to only consider
outputs with enough available fake outs in the first place.

src/wallet/wallet2.cpp

@@ -4119,7 +4119,8 @@ std::vector<wallet2::pending_tx> wallet2::create_transactions_2(std::vector<cryp
   THROW_WALLET_EXCEPTION_IF(needed_money == 0, error::zero_destination);
 
   // gather all our dust and non dust outputs
-  for (size_t i = 0; i < m_transfers.size(); ++i)
+  const std::vector<size_t> unused_indices = select_available_outputs_from_histogram(fake_outs_count + 1, true, true, trusted_daemon);
+  for (size_t i: unused_indices)
   {
     const transfer_details& td = m_transfers[i];
     if (!td.m_spent && (use_rct ? true : !td.is_rct()) && is_transfer_unlocked(td))