[geary: 39/66] Minor fix to last commit

[Michael Gratton <mjog src gnome org>]

commit 43ecc3529856e91fe1f459f3e1bbde740aec4d2d
Author: Chris Heywood <15127-creywood users noreply gitlab gnome org>
Date:   Fri Jan 10 18:08:37 2020 +0100

    Minor fix to last commit

 src/engine/imap-engine/imap-engine-account-synchronizer.vala | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/engine/imap-engine/imap-engine-account-synchronizer.vala 
b/src/engine/imap-engine/imap-engine-account-synchronizer.vala
index cd27a6708..ccaa48881 100644
--- a/src/engine/imap-engine/imap-engine-account-synchronizer.vala
+++ b/src/engine/imap-engine/imap-engine-account-synchronizer.vala
@@ -103,13 +103,13 @@ private class Geary.ImapEngine.AccountSynchronizer :
         }
     }
 
-    private void old_messages_background_cleanup(GLib.Cancellable cancellable) {
+    private void old_messages_background_cleanup(GLib.Cancellable? cancellable) {
         if (this.account.is_open()) {
             SyncDetachMonitor monitor = new SyncDetachMonitor();
             send_all(this.account.list_folders(), false, true, monitor);
             monitor.initialised = true;
             monitor.completed.connect((messages_detached) => {
-                if (cancellable.is_cancelled())
+                if (cancellable != null && cancellable.is_cancelled())
                     return;
 
                 // Run GC. Reap is forced if messages were detached. Vacuum