Replaces return"" by return QString()
Replaces return"" by return QString()

It's faster and cleaner.
        QString().isEmpty();            // returns true
        QString().isNull();             // returns true
So replacing "" by QString() will not brake existing code.

Signed-off-by: Luís Pereira <95d1463b1ff9eef535e39fb0d755bc242cfcea61@gmail.com>

lxde/liblxqt,rbazaud/liblxqt,ThomasVie/liblxqt,stefonarch/liblxqt,lxde/liblxqt,stefonarch/liblxqt,gilir/liblxqt-qt5,pmattern/liblxqt,pmattern/liblxqt,rbazaud/liblxqt,gilir/liblxqt-qt5,ThomasVie/liblxqt