[geary] Fix warning introduced by commit 7954a224.

[Michael Gratton <mjog src gnome org>]

commit 589c9da3eb3dca2157cf6dd4fb10a8a31f90410d
Author: Michael James Gratton <mike vee net>
Date:   Sat Apr 14 21:02:20 2018 +1000

    Fix warning introduced by commit 7954a224.

 src/client/composer/composer-widget.vala |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/client/composer/composer-widget.vala b/src/client/composer/composer-widget.vala
index fa427c3..ec2d2c3 100644
--- a/src/client/composer/composer-widget.vala
+++ b/src/client/composer/composer-widget.vala
@@ -2129,7 +2129,7 @@ public class ComposerWidget : Gtk.EventBox {
                         this.editor.update_signature(this.load_signature.end(res));
                     });
                 load_entry_completions();
-                reopen_draft_manager_async();
+                this.reopen_draft_manager_async.begin();
             }
         }
     }