[evolution] Add safety checks for `file_info` into emfe_attachment_format()

[Milan Crha <mcrha src gnome org>]

commit b4ca0ea46f5037fcd92592e30a8e0223af59ee34
Author: Milan Crha <mcrha redhat com>
Date:   Wed Aug 12 11:45:13 2015 +0200

    Add safety checks for `file_info` into emfe_attachment_format()
    
    This could rise when printing. The attachment print can be called
    multiple times, sometimes with not set `file_info` yet, which resulted
    in runtime warnings.

 em-format/e-mail-formatter-attachment.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)
---
diff --git a/em-format/e-mail-formatter-attachment.c b/em-format/e-mail-formatter-attachment.c
index 48f4183..dc60514 100644
--- a/em-format/e-mail-formatter-attachment.c
+++ b/em-format/e-mail-formatter-attachment.c
@@ -205,7 +205,10 @@ emfe_attachment_format (EMailFormatterExtension *extension,
                                E_MAIL_PART_ATTACHMENT (part));
 
                        file_info = e_attachment_ref_file_info (attachment);
-                       display_name = g_file_info_get_display_name (file_info);
+                       if (file_info)
+                               display_name = g_file_info_get_display_name (file_info);
+                       else
+                               display_name = "";
 
                        description = e_attachment_dup_description (attachment);
                        if (description != NULL && *description != '\0') {
@@ -225,8 +228,8 @@ emfe_attachment_format (EMailFormatterExtension *extension,
                        g_free (description);
                        g_free (name);
 
-                       g_object_unref (attachment);
-                       g_object_unref (file_info);
+                       g_clear_object (&attachment);
+                       g_clear_object (&file_info);
                }
 
                head = g_queue_peek_head_link (extensions);