db_lmdb: include chain height when failing to find an output key

To help debugging logs.

src/blockchain_db/lmdb/db_lmdb.cpp

@@ -2933,7 +2933,7 @@ void BlockchainLMDB::get_output_key(const uint64_t &amount, const std::vector<ui
         MDEBUG("Partial result: " << outputs.size() << "/" << offsets.size());
         break;
       }
-      throw1(OUTPUT_DNE((std::string("Attempting to get output pubkey by global index (amount ") + boost::lexical_cast<std::string>(amount) + ", index " + boost::lexical_cast<std::string>(index) + ", count " + boost::lexical_cast<std::string>(get_num_outputs(amount)) + "), but key does not exist").c_str()));
+      throw1(OUTPUT_DNE((std::string("Attempting to get output pubkey by global index (amount ") + boost::lexical_cast<std::string>(amount) + ", index " + boost::lexical_cast<std::string>(index) + ", count " + boost::lexical_cast<std::string>(get_num_outputs(amount)) + "), but key does not exist (current height " + boost::lexical_cast<std::string>(height()) + ")").c_str()));
     }
     else if (get_result)
       throw0(DB_ERROR(lmdb_error("Error attempting to retrieve an output pubkey from the db", get_result).c_str()));