Deadlock in kded whith Qt 5.6

[Aleix Pol]

Hi,
I realized earlier last week that some of my applications were
freezing, it turns out it's because my kded is freezing and any dbus
calls there need to time out (they take 30s to time out btw).

Anyway, here's the backtrace: https://paste.kde.org/pajbfmoh8

I saw David did something in that direction earlier but I couldn't
spot exactly where's the problem, so I decided to report it here,
hoping he'd know what's going on. :D

Thanks!!

Aleix