[aravis] viewer: avoid warning if a camera is not found

[Emmanuel Pacaud <emmanuel src gnome org>]

commit 9b4385fe3ae42029a4a9b2abb0c62ddce5274918
Author: Emmanuel Pacaud <emmanuel gnome org>
Date:   Wed Jun 4 17:55:40 2014 +0200

    viewer: avoid warning if a camera is not found
    
    Partial fix, as any click on the camera control will also emit a warning.
    The complete fix involves a constantl monitoring of the devices, and the
    update of the camera combo box.

 viewer/arvviewer.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/viewer/arvviewer.c b/viewer/arvviewer.c
index 89840df..72560d8 100644
--- a/viewer/arvviewer.c
+++ b/viewer/arvviewer.c
@@ -540,6 +540,8 @@ arv_viewer_select_camera_cb (GtkComboBox *combo_box, ArvViewer *viewer)
        gtk_tree_model_get (GTK_TREE_MODEL (list_store), &iter, 0, &camera_id, -1);
        viewer->camera = arv_camera_new (camera_id);
        g_free (camera_id);
+       if (viewer->camera == NULL)
+               return;
 
        viewer->rotation = 0;
        viewer->stream = arv_camera_create_stream (viewer->camera, NULL, NULL);