qml: Add const to sendrecipient's m_wallet

Author: johnny9

src/qml/models/sendrecipient.h

@@ -63,7 +63,7 @@ class SendRecipient : public QObject
     void validateAddress();
     void validateAmount();
 
-    WalletQmlModel* m_wallet;
+    const WalletQmlModel* m_wallet;
     QString m_address{""};
     QString m_addressError{""};
     QString m_label{""};