TestHandleSegv: also assert that we have a thread

[emaste]

Summary

If get_stopped_thread(... eStopReasonSignal) returns no thread, the thread.IsValid assertion would throw AttributeError: 'NoneType' object has no attribute 'IsValid'.

[labath]

lgtm

test/functionalities/signal/handle-segv/TestHandleSegv.py

def test_inferior_handle_sigsegv_with_dwarf(self):
 
         # launch
         process = target.LaunchSimple(None, None, self.get_process_working_directory())
         self.assertTrue(process, PROCESS_IS_VALID)
         self.assertEqual(process.GetState(), lldb.eStateStopped)
         signo = process.GetUnixSignals().GetSignalNumberFromName("SIGSEGV")
 
         thread = lldbutil.get_stopped_thread(process, lldb.eStopReasonSignal)
-        self.assertTrue(thread.IsValid(), "Thread should be stopped due to a signal")
+        self.assertTrue(thread and thread.IsValid(), "Thread should be stopped due to a signal")
         self.assertTrue(thread.GetStopReasonDataCount() >= 1, "There was data in the event.")
         self.assertEqual(thread.GetStopReasonDataAtIndex(0), signo, "The stop signal was SIGSEGV")
 
         # Continue until we exit.
         process.Continue()
         self.assertEqual(process.GetState(), lldb.eStateExited)
         self.assertEqual(process.GetExitStatus(), 0)
 
 if __name__ == '__main__':
     import atexit
     lldb.SBDebugger.Initialize()
     atexit.register(lambda: lldb.SBDebugger.Terminate())
     unittest2.main()