mutt: Fix error message for attach-message. (closes #3785)

[Brendan Cully]

changeset: 6519:19c3406fbad9
user:      Kevin McCarthy <ke...@8t8.us>
date:      Sat Oct 17 11:15:01 2015 +0800
link:      http://dev.mutt.org/hg/mutt/rev/19c3406fbad9

Fix error message for attach-message. (closes #3785)

Currently if mx_open_mailbox() fails when trying to attach a message,
mutt_perror() is called.  Change this to call mutt_error() instead,
since errno isn't set for all failure cases.

diffs (12 lines):

diff -r 7aa4e6fc6884 -r 19c3406fbad9 compose.c
--- a/compose.c Thu Oct 08 13:17:03 2015 +0200
+++ b/compose.c Sat Oct 17 11:15:01 2015 +0800
@@ -754,7 +754,7 @@
          ctx = mx_open_mailbox (fname, M_READONLY, NULL);
          if (ctx == NULL)
          {
-           mutt_perror (fname);
+           mutt_error (_("Unable to open mailbox %s"), fname);
            break;
          }