GUI: add getter for WalletModel::m_cached_balances field

No need to guard it as it is/will only be accessed from the main thread for now

src/qt/walletmodel.cpp

@@ -126,6 +126,11 @@ void WalletModel::checkBalanceChanged(const interfaces::WalletBalances& new_bala
     }
 }
 
+interfaces::WalletBalances WalletModel::getCachedBalance() const
+{
+    return m_cached_balances;
+}
+
 void WalletModel::updateTransaction()
 {
     // Balance and number of transactions might have changed

src/qt/walletmodel.h

@@ -157,6 +157,9 @@ public:
 
     uint256 getLastBlockProcessed() const;
 
+    // Retrieve the cached wallet balance
+    interfaces::WalletBalances getCachedBalance() const;
+
 private:
     std::unique_ptr<interfaces::Wallet> m_wallet;
     std::unique_ptr<interfaces::Handler> m_handler_unload;