[balsa/autocrypt] Check for NULL message

[Peter Bloomfield <peterb src gnome org>]

commit d0a939688f1a0706810272a5e64dd8b112f21695
Author: Peter Bloomfield <PeterBloomfield bellsouth net>
Date:   Fri Jan 11 09:51:19 2019 -0500

    Check for NULL message
    
    * libbalsa/imap/imap-commands.c (imap_mbox_sort_msgno_client):
      check for NULL message and for a message with a NULL envelope,
      to avoid dereferencing NULL pointers.

 ChangeLog                     | 8 ++++++++
 libbalsa/imap/imap-commands.c | 4 ++++
 2 files changed, 12 insertions(+)
---
diff --git a/ChangeLog b/ChangeLog
index ea52b1176..3fc10471e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2019-01-11  Peter Bloomfield  <pbloomfield bellsouth net>
+
+       Check for NULL message
+
+       * libbalsa/imap/imap-commands.c (imap_mbox_sort_msgno_client):
+       check for NULL message and for a message with a NULL envelope,
+       to avoid dereferencing NULL pointers.
+
 2018-01-10  Albrecht Dreß  <albrecht dress arcor de>
 
        Minor autocrypt fixes
diff --git a/libbalsa/imap/imap-commands.c b/libbalsa/imap/imap-commands.c
index 5d96d817d..19feef702 100644
--- a/libbalsa/imap/imap-commands.c
+++ b/libbalsa/imap/imap-commands.c
@@ -1868,6 +1868,10 @@ imap_mbox_sort_msgno_client(ImapMboxHandle *handle, ImapSortKey key,
   sort_items = g_new(struct SortItem, cnt);
   for(i=0; i<cnt; i++) {
     sort_items[i].msg = imap_mbox_handle_get_msg(handle, msgno[i]);
+    if ((sort_items[i].msg == NULL) || (sort_items[i].msg->envelope == NULL)) {
+      g_free(sort_items);
+      return IMR_BAD;
+    }
     sort_items[i].no  = msgno[i];
   }
   switch(key) {