Crash on exit in QOpenGLVertexArrayObject

After porting an application from Qt 5.6 to Qt 5.12 we found a crash when exiting our application. 

We were able to track down the issue back to commit 1b9af84c1b (QTBUG-70148). This commit added the following check in qtbase/src/gui/opengl/qopenglvertexarrayobject.cpp (line 212):

if (QThread::currentThread() != qGuiApp->thread()) {
  ctx = 0;
} else {

The crash happens because qGuiApp is already set to nullptr before this code is reached.

The problem described in QTBUG-73824 also seems to have the same issue.