blockchain: silence an error getting blocks for pruned nodes

This happens often when a pre-pruning node asks a pruned node
for data it does not have

src/cryptonote_core/blockchain.cpp

@@ -1951,10 +1951,14 @@ bool Blockchain::handle_get_objects(NOTIFY_REQUEST_GET_OBJECTS::request& arg, NO
 
     if (missed_tx_ids.size() != 0)
     {
-      LOG_ERROR("Error retrieving blocks, missed " << missed_tx_ids.size()
-          << " transactions for block with hash: " << get_block_hash(bl.second)
-          << std::endl
-      );
+      // do not display an error if the peer asked for an unpruned block which we are not meant to have
+      if (tools::has_unpruned_block(get_block_height(bl.second), get_current_blockchain_height(), get_blockchain_pruning_seed()))
+      {
+        LOG_ERROR("Error retrieving blocks, missed " << missed_tx_ids.size()
+            << " transactions for block with hash: " << get_block_hash(bl.second)
+            << std::endl
+        );
+      }
 
       // append missed transaction hashes to response missed_ids field,
       // as done below if any standalone transactions were requested