[gnome-boxes] os-database: avoid crash during wizard if loading failed

[Marc-Andre Lureau <malureau src gnome org>]

commit 9748749aa5b4f06adf87db37d14f09d4f836cb07
Author: Marc-Andrà Lureau <marcandre lureau gmail com>
Date:   Mon Sep 3 15:59:33 2012 +0200

    os-database: avoid crash during wizard if loading failed
    
    We can quite easily avoid a crash during wizard if the db couldn't be
    loaded, although this really shouldn't happen.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=683271

 src/media-manager.vala |    3 ++-
 src/os-database.vala   |   12 ++++++++++--
 2 files changed, 12 insertions(+), 3 deletions(-)
---
diff --git a/src/media-manager.vala b/src/media-manager.vala
index de7505e..7159c3a 100644
--- a/src/media-manager.vala
+++ b/src/media-manager.vala
@@ -15,8 +15,9 @@ private class Boxes.MediaManager : Object {
 
     public MediaManager () {
         client = new GUdev.Client ({"block"});
+        os_db = new OSDatabase ();
         try {
-            os_db = new OSDatabase ();
+            os_db.load ();
         } catch (GLib.Error error) {
             critical ("Error fetching default OS database: %s", error.message);
         }
diff --git a/src/os-database.vala b/src/os-database.vala
index 3fd6215..9885b43 100644
--- a/src/os-database.vala
+++ b/src/os-database.vala
@@ -16,7 +16,7 @@ private class Boxes.OSDatabase {
     // dependent on the OS/guest.
     private const int64 DEFAULT_STORAGE = 20 * (int64) GIBIBYTES;
 
-    private Db db;
+    private Db? db;
 
     private static Resources get_default_resources () {
         var resources = new Resources ("whatever", "x86_64");
@@ -28,7 +28,7 @@ private class Boxes.OSDatabase {
         return resources;
     }
 
-    public OSDatabase () throws GLib.Error {
+    public void load () throws GLib.Error {
         var loader = new Loader ();
         loader.process_default_path ();
         loader.process_path (get_logos_db ()); // Load our custom database
@@ -38,12 +38,20 @@ private class Boxes.OSDatabase {
     public async Os? guess_os_from_install_media (string media_path,
                                                   out Media os_media,
                                                   Cancellable? cancellable) throws GLib.Error {
+        os_media = null;
+
+        if (db == null)
+            return null;
+
         var media = yield Media.create_from_location_async (media_path, Priority.DEFAULT, cancellable);
 
         return db.guess_os_from_media (media, out os_media);
     }
 
     public Os get_os_by_id (string id) throws OSDatabaseError {
+        if (db == null)
+            throw new OSDatabaseError.UNKNOWN_OS_ID ("Unknown OS ID '%s'", id);
+
         var os = db.get_os (id);
         if (os == null)
             throw new OSDatabaseError.UNKNOWN_OS_ID ("Unknown OS ID '%s'", id);