BlockchainLMDB: Remove tx outputs in reverse order

Data should be removed in the reverse order it was added.

This matches the order of removal in
blockchain_storage::pop_transaction_from_global_index.

src/blockchain_db/lmdb/db_lmdb.cpp

@@ -722,15 +722,15 @@ void BlockchainLMDB::remove_tx_outputs(const crypto::hash& tx_hash, const transa
     size_t num_elems = 0;
     mdb_cursor_count(cur, &num_elems);
 
-    mdb_cursor_get(cur, &k, &v, MDB_FIRST_DUP);
+    mdb_cursor_get(cur, &k, &v, MDB_LAST_DUP);
 
-    for (uint64_t i = 0; i < num_elems; ++i)
+    for (uint64_t i = num_elems; i > 0; --i)
     {
-      const tx_out tx_output = tx.vout[i];
+      const tx_out tx_output = tx.vout[i-1];
       remove_output(*(const uint64_t*)v.mv_data, tx_output.amount);
-      if (i < num_elems - 1)
+      if (i > 1)
       {
-        mdb_cursor_get(cur, &k, &v, MDB_NEXT_DUP);
+        mdb_cursor_get(cur, &k, &v, MDB_PREV_DUP);
       }
     }
   }