DD4hepSimulation: fix issue when compactFile did not contain a slash

This makes sure a correct URI is passed to the documenthandler (XMLLoader)

DDG4/python/DDSim/DD4hepSimulation.py

@@ -291,7 +291,7 @@ class DD4hepSimulation(object):
     dd4hep.setPrintLevel(self.printLevel)
 
     for compactFile in self.compactFile:
-      kernel.loadGeometry(str("file:" + compactFile))
+      kernel.loadGeometry(str("file:" + os.path.abspath(compactFile)))
     detectorDescription = kernel.detectorDescription()
 
     DDG4.importConstants(detectorDescription)