Invalid style override breaks Qt Quick Control applications (incl. crash)

1. Start Creator with the invalid style override 'kvantum':

   QT_STYLE_OVERRIDE=kvantum ./qtcreator-6.0.2/bin/qtcreator -tcs
   

   On the command line, you can read:

   QApplication: invalid style override 'kvantum' passed, ignoring it.
   	Available styles: Windows, Fusion
   

2. Open the QML-Profiler in Debug mode.
   There's just a white rectangle where the timeline should be.
3. Go to the "Flame Graph" tab.
   There's just a white rectangle where the flame graph should be.
4. Right-click into that rectangle.
   Creator crashes.

Two things seems to be wrong there:

1. Obviously, Creator should not crash.
2. When that style override is being ignored as Creator claims, passing it should not make a difference. Since it does make a difference, it seems to not be ignored properly.