[geary] Fix critical when email without any from addresses loaded from DB.

[Michael Gratton <mjog src gnome org>]

commit 15e6877823a9ea4bcbdce6cc1167825f0347af53
Author: Michael James Gratton <mike vee net>
Date:   Mon Jul 25 18:01:30 2016 +1000

    Fix critical when email without any from addresses loaded from DB.
    
    See bbf5f07 and Bug 768468.

 src/engine/api/geary-email.vala |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/engine/api/geary-email.vala b/src/engine/api/geary-email.vala
index 0b2b1f3..1c72e27 100644
--- a/src/engine/api/geary-email.vala
+++ b/src/engine/api/geary-email.vala
@@ -180,7 +180,7 @@ public class Geary.Email : BaseObject {
      * and From not be identical, and that both From and ReplyTo are
      * optional.
      */
-    public void set_originators(Geary.RFC822.MailboxAddresses from,
+    public void set_originators(Geary.RFC822.MailboxAddresses? from,
                                 Geary.RFC822.MailboxAddress? sender,
                                 Geary.RFC822.MailboxAddresses? reply_to)
         throws RFC822Error {