Bug#711142: gnuplot-qt: zooming with the 'qt' and 'wxt' terminals yields blank contents

[Vincent Lefevre]

Control: retitle 711142 gnuplot-qt: zooming with the 'wxt' terminal doesn't work with -persist

Only the retitle wasn't taken into account.
Changed it again (and fixed it).

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Vincent Lefèvre <vincent at vinc17.net> - Web: <https://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)