Fix variable shadowing in qt/paymentserver.cpp
Fix variable shadowing in qt/paymentserver.cpp

qt/paymentserver.cpp:838:51: warning: declaration shadows a field of 'PaymentServer' [-Wshadow]
void PaymentServer::setOptionsModel(OptionsModel *optionsModel) { this->optionsModel = optionsModel; }
                                                  ^
./qt/paymentserver.h:153:19: note: previous declaration is here
    OptionsModel *optionsModel;
                  ^

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