fix NameError in the madgraph-in-PYTHONPATH guard of the launchers

Both bin/madevent (LO) and bin/aMCatNLO (NLO) import only `logging`, but
the guard body called `logger.getLogger(...)`. The name `logger` is never
bound in either script, so instead of warning that madgraph is importable
the launcher died with

    NameError: name 'logger' is not defined

Use `logging.getLogger('madgraph')` so the intended error is emitted.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: oliviermattelaer

Template/LO/bin/madevent

@@ -185,7 +185,7 @@ try:
 except ImportError:
     pass
 else:
-    logger.getLogger('madgraph').error('Looks like you do have madgraph in your PYTHONPATH (or you run this executable from the main MG5aMC directory). This executable will likely not work in such case.')
+    logging.getLogger('madgraph').error('Looks like you do have madgraph in your PYTHONPATH (or you run this executable from the main MG5aMC directory). This executable will likely not work in such case.')
 
 
 

Template/NLO/bin/aMCatNLO

@@ -170,7 +170,7 @@ try:
 except ImportError:
     pass
 else:
-    logger.getLogger('madgraph').error('Looks like you do have madgraph in your PYTHONPATH (or you run this executable    from the main MG5aMC directory). This executable will likely not work in such case.')
+    logging.getLogger('madgraph').error('Looks like you do have madgraph in your PYTHONPATH (or you run this executable    from the main MG5aMC directory). This executable will likely not work in such case.')
 
 
 # Call the cmd interface main loop