[pdfmod] Fix crash on page click due to ExportImagesAction (bgo#631889)

[Gabriel Burt <gburt src gnome org>]

commit 7601244cf5253ae42797c01d60b8b6ebc65c9820
Author: Gabriel Burt <gabriel burt gmail com>
Date:   Thu Mar 3 11:43:25 2011 -0600

    Fix crash on page click due to ExportImagesAction (bgo#631889)
    
    If the /Filter of an image is an array, say [/FlateDecode, /DctDecode]
    we would crash, since we were expecting just one of those.  We now
    ignore such images (still only handling PNG and JPEG files).

 src/PdfMod/Pdf/Actions/ExportImagesAction.cs |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/src/PdfMod/Pdf/Actions/ExportImagesAction.cs b/src/PdfMod/Pdf/Actions/ExportImagesAction.cs
index ff45dbf..8363b2d 100644
--- a/src/PdfMod/Pdf/Actions/ExportImagesAction.cs
+++ b/src/PdfMod/Pdf/Actions/ExportImagesAction.cs
@@ -104,7 +104,8 @@ namespace PdfMod.Pdf.Actions
 
         bool IsExportable (ImageInfo image)
         {
-            var filter = image.ImageObject.Elements.GetName("/Filter");
+            var filter_obj = image.ImageObject.Elements["/Filter"];
+            var filter = filter_obj == null ? "" : filter_obj.ToString ();
             return filter == "/DCTDecode" || filter == "/FlateDecode";
         }
 
@@ -113,7 +114,8 @@ namespace PdfMod.Pdf.Actions
         /// </summary>
         void Export (ImageInfo image, string to_path)
         {
-            string filter = image.ImageObject.Elements.GetName("/Filter");
+            var filter_obj = image.ImageObject.Elements["/Filter"];
+            var filter = filter_obj == null ? "" : filter_obj.ToString ();
             switch (filter) {
                 case "/DCTDecode":
                     ExportJpegImage (image, GetFilename (image, to_path, "jpg"));