[gnome-software] Don't perform a lookup when the category is NULL

[William Hua <williamhua src gnome org>]

commit 9f3fc8fc3f085b35d948d29b5ed8670b8e590fe6
Author: William Hua <william hua canonical com>
Date:   Mon Feb 29 17:44:40 2016 -0500

    Don't perform a lookup when the category is NULL
    
    Some desktop files like fslint.desktop have a NULL category entry that
    causes a segfault when trying to do a lookup in get_app_folder ().

 src/gs-folders.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)
---
diff --git a/src/gs-folders.c b/src/gs-folders.c
index f4abca4..02768e4 100644
--- a/src/gs-folders.c
+++ b/src/gs-folders.c
@@ -450,12 +450,17 @@ static GsFolder *
 get_app_folder (GsFolders *folders, const gchar *app, GPtrArray *categories)
 {
        GsFolder *folder;
+       const gchar *category;
        guint i;
 
        folder = g_hash_table_lookup (folders->apps, app);
        if (!folder && categories) {
                for (i = 0; i < categories->len; i++) {
-                       folder = g_hash_table_lookup (folders->categories, g_ptr_array_index (categories, i));
+                       category = g_ptr_array_index (categories, i);
+                       if (category == NULL)
+                               continue;
+
+                       folder = g_hash_table_lookup (folders->categories, category);
                        if (folder) {
                                break;
                        }