[xslt] wrong fix in transform.c

[Nathan Myers <ncm-xml cantrip org>]

Earlier I sent in a suggested patch to libxslt/transform.c:

  http://mail.gnome.org/archives/xml/2002-August/msg00068.html

Unfortunately it appears that in libxslt-1.0.20, that patch
was not applied, and that instead a similar patch was applied
elsewhere.  

It seems to me that the change that was applied was harmless but
effectless.  Anyhow the actual patch cited is necessary to prevent
a crash in my application.  The bug it fixes might best be described
as a double-free memory management error.

Nathan Myers