Fix Qt deprecation warn for setConfirmOverwrite()

Fix Qt deprecation warn for setConfirmOverwrite()

Fix the following warning:

  error: ‘void QFileDialog::setConfirmOverwrite(bool)’ is deprecated: Use setOption(DontConfirmOverwrite, !enabled) instead [-Werror=deprecated-declarations]

Note in the change that "false" changes to "true" because the option
is *Dont*ConfirmOverwrite.

QFileDialog::setConfirmOverwrite() is obsolete at least since 4.8
and QFileDialog::setOption() is available since 4.5 [1].

[1] https://doc.qt.io/archives/qt-4.8/qfiledialog-obsolete.html
[2] https://doc.qt.io/qt-5/qfiledialog.html#setOption