blockchain_db: store key images for tx without outputs too

src/blockchain_db/blockchain_db.cpp

@@ -60,8 +60,6 @@ void BlockchainDB::add_transaction(const crypto::hash& blk_hash, const transacti
 
   // iterate tx.vout using indices instead of C++11 foreach syntax because
   // we need the index
-  if (tx.vout.size() != 0)  // it may be technically possible for a tx to have no outputs
-  {
   for (uint64_t i = 0; i < tx.vout.size(); ++i)
   {
     add_output(tx_hash, tx.vout[i], i, tx.unlock_time);
@@ -75,7 +73,6 @@ void BlockchainDB::add_transaction(const crypto::hash& blk_hash, const transacti
     }
   }
 }
-}
 
 uint64_t BlockchainDB::add_block( const block& blk
                                 , const size_t& block_size