QGLFormat::openGLVersionFlags() aborts if no screen available

Crash happens if QGLFormat::openGLVersionFlags() is called before screeen is available. Possible scenario on Mac Mavericks when swithcing users and application is Login Item application.

crash log:

Crashed Thread:  0  Dispatch queue: com.apple.main-thread
Exception Type:  EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: EXC_I386_GPFLT
0   libobjc.A.dylib               	0x00007fff8f952097 objc_msgSend + 23
1   libqcocoa.dylib               	0x0000000104f169c2 0x104f00000 + 92610
2   libqcocoa.dylib               	0x0000000104f0810e 0x104f00000 + 33038
3   QtGui                         	0x000000010029e9ed QOpenGLContext::create() + 45
4   QtOpenGL                      	0x0000000101a5dfe2 0x101a2b000 + 208866
5   QtOpenGL                      	0x0000000101a2f257 QGLFormat::openGLVersionFlags() + 119

Relates to QTBUG-37876. But crashes to different place.

To reproduce:

• System: Maverics 10.9 OSX
• Qt version: 5.2.0

For the both case please find Steps to reproduce:
1) Build the sample application using Qt 5.2.0 and you get a binary image example sample.app
2) So copy this sample.app into /Application folder so that all users can run this application
3) Make this application as a login item for two or three users. For this go to System Preferences -> select Login items tab -> add the application name sample.app. Do this for all other users as well.
4) After adding the sample.app as login item for all users,then logout from all users.
5) Now start login to first user and then switch between different users.Then you will get crash.