Do not let 'NO_TRACEBACK' escape.

Author: fangerer

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/nodes/control/TopLevelExceptionHandler.java

@@ -127,7 +127,9 @@ public Object execute(VirtualFrame frame) {
                 // we cannot reify at this point because we have no Python frame; so create the full
                 // traceback chain
                 PTraceback tbHead = GetTracebackNextNode.createTracebackChain(e, materializeFrameNode, factory());
-                e.getExceptionObject().setTraceback(tbHead);
+                if (tbHead != PTraceback.NO_TRACEBACK) {
+                    e.getExceptionObject().setTraceback(tbHead);
+                }
                 printExc(frame, e);
                 if (PythonOptions.getOption(context.get(), PythonOptions.WithJavaStacktrace)) {
                     printStackTrace(e);