[libxslt] Fix possible NULL pointer deref in preproc.c

[Nick Wellnhofer <nwellnhof src gnome org>]

commit f76aadd3c396460236b63eb86dfc828ceba7ba53
Author: mahendra.n <mahendra n samsung com>
Date:   Sun Dec 13 18:44:14 2015 +0100

    Fix possible NULL pointer deref in preproc.c
    
    Fixes bug #757617.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=757617

 libxslt/preproc.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/libxslt/preproc.c b/libxslt/preproc.c
index 7f69325..955b3b0 100644
--- a/libxslt/preproc.c
+++ b/libxslt/preproc.c
@@ -1305,7 +1305,8 @@ xsltGetQNameProperty(xsltStylesheetPtr style, xmlNodePtr inst,
            if (prop == NULL) {
                style->errors++;
            } else {
-               *localName = prop;
+               if (localName)
+                   *localName = prop;
                if (hasProp)
                    *hasProp = 1;
                if (URI != NULL) {