qtdeclarative backport suggestion

[Nicolas Fella]

Hi,

https://codereview.qt-project.org/c/qt/qtdeclarative/+/704031 fixes a 
frequent crash in plasmashell: https://bugs.kde.org/show_bug.cgi?id=513527

It's scheduled for 6.10.3, but I'd recommend backporting it.

Cheers

Nico