[2 krita picks] Check whether there is a QGestureRecognizer at all / Do not crash if the foundry name is an empty space

I became aware that there is a krita Qt5 fork, so I've skimmed through their commits and found two obvious single-line fixes, but they are not (Qt-company-)upstream yet.

Bugs:

• https://bugs.kde.org/show_bug.cgi?id=421707
• https://bugs.kde.org/show_bug.cgi?id=430220

@rempt: Do you think these could be sent upstream (for Qt6) so they can be properly picked here?