wallet: maintain SPK consistency on internal flag change

Author: S3RK

src/wallet/wallet.cpp

@@ -3153,12 +3153,21 @@ void CWallet::AddActiveScriptPubKeyMan(uint256 id, OutputType type, bool interna
 
 void CWallet::LoadActiveScriptPubKeyMan(uint256 id, OutputType type, bool internal)
 {
+    // Activating ScriptPubKeyManager for a given output and change type is incompatible with legacy wallets.
+    // Legacy wallets have only one ScriptPubKeyManager and it's active for all output and change types.
+    Assert(IsWalletFlagSet(WALLET_FLAG_DESCRIPTORS));
+
     WalletLogPrintf("Setting spkMan to active: id = %s, type = %d, internal = %d\n", id.ToString(), static_cast<int>(type), static_cast<int>(internal));
     auto& spk_mans = internal ? m_internal_spk_managers : m_external_spk_managers;
+    auto& spk_mans_other = internal ? m_external_spk_managers : m_internal_spk_managers;
     auto spk_man = m_spk_managers.at(id).get();
     spk_man->SetInternal(internal);
     spk_mans[type] = spk_man;
 
+    if (spk_mans_other[type] == spk_man) {
+        spk_mans_other[type] = nullptr;
+    }
+
     NotifyCanGetAddressesChanged();
 }