use current height - 1 for top block height in err msgs

src/rpc/core_rpc_server.cpp

@@ -1010,7 +1010,7 @@ namespace cryptonote
     if(m_core.get_current_blockchain_height() <= h)
     {
       error_resp.code = CORE_RPC_ERROR_CODE_TOO_BIG_HEIGHT;
-      error_resp.message = std::string("Too big height: ") + std::to_string(h) + ", current blockchain height = " +  std::to_string(m_core.get_current_blockchain_height());
+      error_resp.message = std::string("Requested block height: ") + std::to_string(h) + " greater than current top block height: " +  std::to_string(m_core.get_current_blockchain_height() - 1);
     }
     res = string_tools::pod_to_hex(m_core.get_block_id_by_height(h));
     return true;
@@ -1457,7 +1457,7 @@ namespace cryptonote
     if(m_core.get_current_blockchain_height() <= req.height)
     {
       error_resp.code = CORE_RPC_ERROR_CODE_TOO_BIG_HEIGHT;
-      error_resp.message = std::string("Too big height: ") + std::to_string(req.height) + ", current blockchain height = " +  std::to_string(m_core.get_current_blockchain_height());
+      error_resp.message = std::string("Requested block height: ") + std::to_string(req.height) + " greater than current top block height: " +  std::to_string(m_core.get_current_blockchain_height() - 1);
       return false;
     }
     crypto::hash block_hash = m_core.get_block_id_by_height(req.height);
@@ -1502,7 +1502,7 @@ namespace cryptonote
       if(m_core.get_current_blockchain_height() <= req.height)
       {
         error_resp.code = CORE_RPC_ERROR_CODE_TOO_BIG_HEIGHT;
-        error_resp.message = std::string("Too big height: ") + std::to_string(req.height) + ", current blockchain height = " +  std::to_string(m_core.get_current_blockchain_height());
+        error_resp.message = std::string("Requested block height: ") + std::to_string(req.height) + " greater than current top block height: " +  std::to_string(m_core.get_current_blockchain_height() - 1);
         return false;
       }
       block_hash = m_core.get_block_id_by_height(req.height);