[Qt] constify first parameter of processPaymentRequest()

src/qt/paymentserver.cpp

@@ -526,7 +526,7 @@ bool PaymentServer::readPaymentRequestFromFile(const QString& filename, PaymentR
     return request.parse(data);
 }
 
-bool PaymentServer::processPaymentRequest(PaymentRequestPlus& request, SendCoinsRecipient& recipient)
+bool PaymentServer::processPaymentRequest(const PaymentRequestPlus& request, SendCoinsRecipient& recipient)
 {
     if (!optionsModel)
         return false;

src/qt/paymentserver.h

@@ -131,7 +131,7 @@ protected:
     bool eventFilter(QObject *object, QEvent *event);
 
 private:
-    bool processPaymentRequest(PaymentRequestPlus& request, SendCoinsRecipient& recipient);
+    bool processPaymentRequest(const PaymentRequestPlus& request, SendCoinsRecipient& recipient);
     void fetchRequest(const QUrl& url);
 
     // Setup networking