DDSim: Fix bug in enablePrimaryHandler

Need to return the value
Kept DDg4ParticleGun from working

DDSim/DD4hepSimulation.py

@@ -692,6 +692,7 @@ SIM = DD4hepSimulation()
       print "Enabling the PrimaryHandler"
     else:
       print "Disabling the PrimaryHandler"
+    return enablePrimaryHandler
 
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 ### MODULE FUNCTIONS GO HERE