BUG: Ensure python script argument are not loaded as image. Fixes #3463

Co-authored-by: Jean-Christophe Fillion-Robin <jchris.fillionr@kitware.com>

From: Felix Veysseyre <felix.veysseyre@kitware.com>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22658 3bd1e089-480b-0410-8dfb-8563597acbee