blockchain: forbid bulletproof types before v8

They were already forbidden implicitely, but let's make that
explicit for robustness

src/cryptonote_core/blockchain.cpp

@@ -2407,7 +2407,8 @@ bool Blockchain::check_tx_outputs(const transaction& tx, tx_verification_context
 
   // from v8, allow bulletproofs
   if (hf_version < 8) {
-    if (!tx.rct_signatures.p.bulletproofs.empty())
+    const bool bulletproof = tx.rct_signatures.type == rct::RCTTypeFullBulletproof || tx.rct_signatures.type == rct::RCTTypeSimpleBulletproof;
+    if (bulletproof || !tx.rct_signatures.p.bulletproofs.empty())
     {
       MERROR("Bulletproofs are not allowed before v8");
       tvc.m_invalid_output = true;