Don't access qApp directly from Platform's ctor

QApplication might not be created yet, so delay it
With a timer for now. Don't guarantee this will stay.
Explicit init by the user might be an alternative.

src/qtquick/Platform_qtquick.h

@@ -24,6 +24,9 @@ public:
     ~Platform_qtquick() override;
     const char *name() const override;
     std::shared_ptr<ViewWrapper> focusedView() const override;
+
+private:
+    void init();
 };
 
 }