wallet: Set upgraded descriptor cache flag for newly created wallets

New wallets always have these upgraded. As a belt-and-suspenders, do the
upgrade as well, but it should not be necessary.

Note that while WalletBatch::LoadWallet also does the upgrade, because
newly created wallets do not have the descriptor flag set yet, the
upgrade does not run and set the flag.

Author: achow101

src/wallet/wallet.cpp

@@ -2921,6 +2921,8 @@ std::shared_ptr<CWallet> CWallet::Create(WalletContext& context, const std::stri
         if ((wallet_creation_flags & WALLET_FLAG_EXTERNAL_SIGNER) || !(wallet_creation_flags & (WALLET_FLAG_DISABLE_PRIVATE_KEYS | WALLET_FLAG_BLANK_WALLET))) {
             if (walletInstance->IsWalletFlagSet(WALLET_FLAG_DESCRIPTORS)) {
                 walletInstance->SetupDescriptorScriptPubKeyMans();
+                // Ensure that the upgraded flag is set and that caches can support this feature.
+                walletInstance->UpgradeDescriptorCache();
                 // SetupDescriptorScriptPubKeyMans already calls SetupGeneration for us so we don't need to call SetupGeneration separately
             } else {
                 // Legacy wallets need SetupGeneration here.