gui: do not add a console logger when there is no sys.stdout

Change-Id: Icfd39bd508b5d482c902e6e781cbc557085b0c2e
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/34829
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Georg Brandl <g.brandl@fz-juelich.de>

bin/frappy-gui

@@ -64,6 +64,7 @@ def main(argv=None):
     loglevel = logging.DEBUG if args.debug else (logging.ERROR if args.quiet else logging.INFO)
     logger = logging.getLogger('gui')
     logger.setLevel(logging.DEBUG)
+    if sys.stdout is not None:
         console = ColoredConsoleHandler()
         console.setLevel(loglevel)
         logger.addHandler(console)