wallet2: key image import fixes

- return the right output data when offset is not zero
- do not consider import failed if result height is zero
  (it can be 0 if unknown)
- select the right tx pubkey when using subaddresses (it's faster,
  and we might select the wrong one if we got an output using one
  of the additional tx keys)
- account for skipped outputs for spent/unspent balance info

"spent" is arguably wrong, since it will count spent change
multiple times as it goes through receive/spend cycles.

src/simplewallet/simplewallet.cpp

@@ -8597,13 +8597,8 @@ bool simple_wallet::import_key_images(const std::vector<std::string> &args)
   {
     uint64_t spent = 0, unspent = 0;
     uint64_t height = m_wallet->import_key_images(filename, spent, unspent);
-    if (height > 0)
-    {
-      success_msg_writer() << "Signed key images imported to height " << height << ", "
-          << print_money(spent) << " spent, " << print_money(unspent) << " unspent"; 
-    } else {
-      fail_msg_writer() << "Failed to import key images";
-    }
+    success_msg_writer() << "Signed key images imported to height " << height << ", "
+        << print_money(spent) << " spent, " << print_money(unspent) << " unspent"; 
   }
   catch (const std::exception &e)
   {

src/wallet/wallet2.cpp

@@ -11002,15 +11002,6 @@ crypto::public_key wallet2::get_tx_pub_key_from_received_outs(const tools::walle
   size_t pk_index = 0;
   hw::device &hwdev = m_account.get_device();
 
-  const std::vector<crypto::public_key> additional_tx_pub_keys = get_additional_tx_pub_keys_from_extra(td.m_tx);
-  std::vector<crypto::key_derivation> additional_derivations;
-  for (size_t i = 0; i < additional_tx_pub_keys.size(); ++i)
-  {
-    additional_derivations.push_back({});
-    bool r = hwdev.generate_key_derivation(additional_tx_pub_keys[i], keys.m_view_secret_key, additional_derivations.back());
-    THROW_WALLET_EXCEPTION_IF(!r, error::wallet_internal_error, "Failed to generate key derivation");
-  }
-
   while (find_tx_extra_field_by_type(tx_extra_fields, pub_key_field, pk_index++)) {
     const crypto::public_key tx_pub_key = pub_key_field.pub_key;
     crypto::key_derivation derivation;
@@ -11020,16 +11011,15 @@ crypto::public_key wallet2::get_tx_pub_key_from_received_outs(const tools::walle
     for (size_t i = 0; i < td.m_tx.vout.size(); ++i)
     {
       tx_scan_info_t tx_scan_info;
-      check_acc_out_precomp(td.m_tx.vout[i], derivation, additional_derivations, i, tx_scan_info);
+      check_acc_out_precomp(td.m_tx.vout[i], derivation, {}, i, tx_scan_info);
       if (!tx_scan_info.error && tx_scan_info.received)
         return tx_pub_key;
     }
   }
 
-  // we found no key yielding an output
-  THROW_WALLET_EXCEPTION_IF(true, error::wallet_internal_error,
-      "Public key yielding at least one output wasn't found in the transaction extra");
-  return crypto::null_pkey;
+  // we found no key yielding an output, but it might be in the additional
+  // tx pub keys only, which we do not need to check, so return the first one
+  return tx_pub_key;
 }
 
 bool wallet2::export_key_images(const std::string &filename) const
@@ -11271,6 +11261,17 @@ uint64_t wallet2::import_key_images(const std::vector<std::pair<crypto::key_imag
   }
   PERF_TIMER_STOP(import_key_images_C);
 
+  // accumulate outputs before the updated data
+  for(size_t i = 0; i < offset; ++i)
+  {
+    const transfer_details &td = m_transfers[i];
+    uint64_t amount = td.amount();
+    if (td.m_spent)
+      spent += amount;
+    else
+      unspent += amount;
+  }
+
   PERF_TIMER_START(import_key_images_D);
   for(size_t i = 0; i < signed_key_images.size(); ++i)
   {
@@ -11433,7 +11434,8 @@ uint64_t wallet2::import_key_images(const std::vector<std::pair<crypto::key_imag
     PERF_TIMER_STOP(import_key_images_G);
   }
 
-  return m_transfers[signed_key_images.size() - 1].m_block_height;
+  // this can be 0 if we do not know the height
+  return m_transfers[signed_key_images.size() + offset - 1].m_block_height;
 }
 
 bool wallet2::import_key_images(std::vector<crypto::key_image> key_images)