[gnome-multi-writer] Fix crash when libusb context creation fails

[Richard Hughes <rhughes src gnome org>]

commit 4e5873e08d5d2e84c2fbd8b1ec0de7e673baf35e
Author: Richard Hughes <richard hughsie com>
Date:   Fri Jan 9 14:21:25 2015 +0000

    Fix crash when libusb context creation fails

 src/gmw-main.c |   16 +++++++++++++---
 1 files changed, 13 insertions(+), 3 deletions(-)
---
diff --git a/src/gmw-main.c b/src/gmw-main.c
index e17b0be..92ddb24 100644
--- a/src/gmw-main.c
+++ b/src/gmw-main.c
@@ -1249,8 +1249,13 @@ gmw_udisks_find_usb_device (GmwPrivate *priv, GmwDevice *device)
 {
        guint8 busnum;
        guint8 devnum;
+       _cleanup_error_free_ GError *error = NULL;
        _cleanup_object_unref_ GUsbDevice *usb_device = NULL;
 
+       /* failed to load GUsb */
+       if (priv->usb_ctx == NULL)
+               return;
+
        /* find the USB device using GUsb */
        if (gmw_device_get_sysfs_path (device) == NULL)
                return;
@@ -1263,9 +1268,9 @@ gmw_udisks_find_usb_device (GmwPrivate *priv, GmwDevice *device)
        usb_device = g_usb_context_find_by_bus_address (priv->usb_ctx,
                                                        busnum,
                                                        devnum,
-                                                       NULL);
+                                                       &error);
        if (usb_device == NULL) {
-               g_warning ("Failed to find %02x:%02x", busnum, devnum);
+               g_warning ("%s", error->message);
                return;
        }
        gmw_device_set_usb_device (device, usb_device);
@@ -1557,7 +1562,12 @@ main (int argc, char **argv)
                                         gmw_thread_pool_sort_func,
                                         priv);
        priv->devices = g_ptr_array_new_with_free_func ((GDestroyNotify) g_object_unref);
-       priv->usb_ctx = g_usb_context_new (NULL);
+       priv->usb_ctx = g_usb_context_new (&error);
+       if (priv->usb_ctx == NULL) {
+               status = EXIT_FAILURE;
+               g_print ("Failed to load libusb: %s\n", error->message);
+               goto out;
+       }
 
        /* connect to UDisks */
        udisks_client_new (NULL, gmw_udisks_client_connect_cb, priv);