[shotwell] Check for failure to render video thumbnail: Bug #738245

[Jim Nelson <jnelson src gnome org>]

commit 2ae25e17ca131e848ae708a1c01ff68e7167ee5a
Author: Jim Nelson <jim yorba org>
Date:   Fri Oct 24 13:43:36 2014 -0700

    Check for failure to render video thumbnail: Bug #738245
    
    As part of a user reporting problems, their trace indicated that
    the GStreamer buffer holding the video thumbnail can sometimes come
    back null.  shotwell-video-thumbnailer wasn't checking for this
    possibility.

 thumbnailer/shotwell-video-thumbnailer.vala |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)
---
diff --git a/thumbnailer/shotwell-video-thumbnailer.vala b/thumbnailer/shotwell-video-thumbnailer.vala
index 5b8b89a..93db2aa 100644
--- a/thumbnailer/shotwell-video-thumbnailer.vala
+++ b/thumbnailer/shotwell-video-thumbnailer.vala
@@ -104,7 +104,12 @@ class ShotwellThumbnailer {
 
                 buffer = sample.get_buffer();
                 buffer.map(out mapinfo, Gst.MapFlags.READ);
-
+                
+                if (mapinfo.data == null || mapinfo.data.length == 0) {
+                    stderr.printf("Could not get snapshot data buffer\n");
+                    return 7;
+                }
+                
                 // Create pixmap from buffer and save, gstreamer video buffers have a stride
                 // that is rounded up to the nearest multiple of 4.
                 pixbuf = new Gdk.Pixbuf.from_data(mapinfo.data, Gdk.Colorspace.RGB, false, 8,