[easytag] Avoid crash when saving unknown image types

[David King <davidk src gnome org>]

commit 6563a0989a6d35d618a950262bd81d2ac50ed0ed
Author: David King <amigadave amigadave com>
Date:   Fri Mar 7 22:41:43 2014 +0000

    Avoid crash when saving unknown image types
    
    https://retrace.fedoraproject.org/faf/problems/1586225/

 src/picture.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/src/picture.c b/src/picture.c
index b6b8f26..8e74b93 100644
--- a/src/picture.c
+++ b/src/picture.c
@@ -988,7 +988,8 @@ const gchar *Picture_Mime_Type_String (Picture_Format format)
         case PICTURE_FORMAT_PNG:
             return "image/png";
         default:
-            return NULL;
+            g_debug ("%s", "Unrecognised image MIME type");
+            return "application/octet-stream";
     }
 }