[gnome-software/gnome-3-26] Do not crash when a plugin adds an app with NULL id

[Kalev Lember <klember src gnome org>]

commit 969c6e5487b398c2f7c1fb8c8a3437e5c365810d
Author: Kalev Lember <klember redhat com>
Date:   Tue Jan 2 22:17:49 2018 +0100

    Do not crash when a plugin adds an app with NULL id
    
    https://retrace.fedoraproject.org/faf/problems/3188252/ points to the
    direction of the fwupd plugin: it is passing a NULL id to
    gs_plugin_cache_add, which leads to a crash GHashTable code, trying to
    g_str_hash the NULL string.
    
    This commit adds a missing g_return_if_fail to gs_plugin_cache_add to
    guard against that. We should figure out what's wrong in the fwupd
    plugin, but this should at least fix the user facing crash in the mean
    time.

 lib/gs-plugin.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/lib/gs-plugin.c b/lib/gs-plugin.c
index d844c46..f354022 100644
--- a/lib/gs-plugin.c
+++ b/lib/gs-plugin.c
@@ -1540,6 +1540,8 @@ gs_plugin_cache_add (GsPlugin *plugin, const gchar *key, GsApp *app)
        if (key == NULL)
                key = gs_app_get_unique_id (app);
 
+       g_return_if_fail (key != NULL);
+
        /* global, so using internal unique_id */
        if (gs_plugin_has_flags (plugin, GS_PLUGIN_FLAGS_GLOBAL_CACHE)) {
                if (!as_utils_unique_id_valid (key)) {