blockchain: fix pow skipping for old blocks without precalc hash

src/cryptonote_core/blockchain.cpp

@@ -4049,8 +4049,8 @@ leave:
       MCINFO("verify", "No pre-validated hash at height " << blockchain_height << ", verifying fully");
     }
   }
-  else
 #endif
+  if (!fast_check)
   {
     auto it = m_blocks_longhash_table.find(id);
     if (it != m_blocks_longhash_table.end())