catch the appropriate exception, if a setting is not explicitely defined

git-svn-id: https://pycam.svn.sourceforge.net/svnroot/pycam/trunk@472 bbaffbd6-741e-11dd-a85d-61de82d9cad9

src/pycam/Gui/Settings.py

@@ -399,7 +399,7 @@ process: 3
         elif value_type == object:
             try:
                 return lists[key].index(value)
-            except IndexError:
+            except ValueError:
                 return None
         else:
             return str(value_type(value))