[gnome-epub-thumbnailer] main: Fix crashes when we cannot find cover info

[Bastien Nocera <hadess src gnome org>]

commit 0fd97b89dd5f0e3c87bf4a39113b981c6b405926
Author: Bastien Nocera <hadess hadess net>
Date:   Sat Jul 13 14:26:41 2013 +0200

    main: Fix crashes when we cannot find cover info
    
    In the metadata.

 gnome-epub-thumbnailer.c |   25 ++++++++++++++-----------
 1 files changed, 14 insertions(+), 11 deletions(-)
---
diff --git a/gnome-epub-thumbnailer.c b/gnome-epub-thumbnailer.c
index 21f7ae3..6005e02 100644
--- a/gnome-epub-thumbnailer.c
+++ b/gnome-epub-thumbnailer.c
@@ -139,23 +139,26 @@ get_prop_for_xpath (xmlDocPtr           doc,
 {
        xmlXPathObjectPtr xpath_obj;
        xmlNodePtr cur;
-       xmlChar *prop;
-       char *ret;
+       char *ret = NULL;
 
        xpath_obj = xmlXPathEvalExpression (BAD_CAST (path), xpath_ctx);
        if (xpath_obj == NULL)
                return NULL;
-       if (xpath_obj->nodesetval == NULL) {
-               xmlXPathFreeObject (xpath_obj);
-               return NULL;
-       }
+       if (xpath_obj->nodesetval == NULL ||
+           xpath_obj->nodesetval->nodeTab == NULL)
+               goto bail;
        cur = xpath_obj->nodesetval->nodeTab[0];
-       prop = xmlGetProp (cur, BAD_CAST (name));
-       ret = NULL;
-       if (prop) {
-               ret = g_strdup ((const char *) prop);
-               xmlFree (prop);
+       if (cur != NULL) {
+               xmlChar *prop;
+
+               prop = xmlGetProp (cur, BAD_CAST (name));
+               if (prop) {
+                       ret = g_strdup ((const char *) prop);
+                       xmlFree (prop);
+               }
        }
+
+bail:
        xmlXPathFreeObject (xpath_obj);
 
        return ret;