blockchain: match original code early out in rollback_blockchain_switching

src/cryptonote_core/blockchain.cpp

@@ -690,6 +690,12 @@ bool Blockchain::rollback_blockchain_switching(std::list<block>& original_chain,
     LOG_PRINT_L3("Blockchain::" << __func__);
     CRITICAL_REGION_LOCAL(m_blockchain_lock);
 
+    // fail if rollback_height passed is too high
+    if (rollback_height > m_db->height())
+    {
+      return true;
+    }
+
     m_timestamps_and_difficulties_height = 0;
 
     // remove blocks from blockchain until we get back to where we should be.