wallet: Set encrypted_batch to nullptr after delete. Avoid double free in the case of NDEBUG.

Author: practicalswift

src/wallet/wallet.cpp

@@ -687,6 +687,7 @@ bool CWallet::EncryptWallet(const SecureString& strWalletPassphrase)
         {
             encrypted_batch->TxnAbort();
             delete encrypted_batch;
+            encrypted_batch = nullptr;
             // We now probably have half of our keys encrypted in memory, and half not...
             // die and let the user reload the unencrypted wallet.
             assert(false);
@@ -697,6 +698,7 @@ bool CWallet::EncryptWallet(const SecureString& strWalletPassphrase)
 
         if (!encrypted_batch->TxnCommit()) {
             delete encrypted_batch;
+            encrypted_batch = nullptr;
             // We now have keys encrypted in memory, but not on disk...
             // die to avoid confusion and let the user reload the unencrypted wallet.
             assert(false);