initSettingsSetValue: use lambda functions
initSettingsSetValue: use lambda functions

Calling SettingsWidget::commitSettings() saves a whole bunch of values,
which is unnecessary when we've only changed one setting.

Tarsnap/tarsnap-gui,Tarsnap/tarsnap-gui,Tarsnap/tarsnap-gui,Tarsnap/tarsnap-gui,Tarsnap/tarsnap-gui