Strings from the supported_charset_list[] were being copied one by
one to a stack buffer, and then strdup called on that buffer.

Instead, just strdup the original string, without the local copy,
and use a more traditional for loop, so it's easier to figure out
what the code is doing (cleaning up a gcc const-cast warning in
the process).
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Matthieu Herrb <matthieu.herrb@laas.fr>
Backported-to-NX-by: Ulrich Sibiller <uli42@gmx.de>