minor fixes to Blockchain.cpp

src/cryptonote_core/BlockchainDB_impl/db_lmdb.cpp

@@ -1022,7 +1022,7 @@ crypto::hash BlockchainLMDB::get_block_hash_from_height(const uint64_t& height)
   if (get_result == MDB_NOTFOUND)
   {
     LOG_PRINT_L0("Attempted to get hash from height " << height << ", but no such hash exists");
-    throw DB_ERROR("Attempt to get hash from height failed -- block size not in db");
+    throw BLOCK_DNE("Attempt to get hash from height failed -- hash not in db");
   }
   else if (get_result)
   {

src/cryptonote_core/blockchain.cpp

@@ -1541,9 +1541,13 @@ void Blockchain::print_blockchain_index()
 {
   std::stringstream ss;
   CRITICAL_REGION_LOCAL(m_blockchain_lock);
-  for(uint64_t i = 0; i <= m_db->height(); i++)
+  auto height = m_db->height();
+  if (height != 0)
   {
-    ss << "height: " << i << ", hash: " << m_db->get_block_hash_from_height(i);
+    for(uint64_t i = 0; i <= height; i++)
+    {
+      ss << "height: " << i << ", hash: " << m_db->get_block_hash_from_height(i);
+    }
   }
 
   LOG_PRINT_L0("Current blockchain index:" << std::endl