simplify the QSettings write check

simplify the QSettings write check

the previous implementation was supposed to be write-optimized, for cases
when QSettings::setValue() followed by QSettings::sync() is called often.
it turns out that optimizing for reading from the settings without changing
the object is more beneficial as that is often the case.

Signed-off-by: Ivailo Monev <xakepa10@laimg.moc>