[geary: 8/66] Add minor missing cleanup

[Michael Gratton <mjog src gnome org>]

commit ff6c45c29c2b4d38988a3921e97bbad7648958cb
Author: Chris Heywood <15127-creywood users noreply gitlab gnome org>
Date:   Wed Jan 8 11:50:54 2020 +0100

    Add minor missing cleanup
    
    this.gc would previously never have been released if GC reap wasn't
    recommended and run

 src/engine/imap-db/imap-db-database.vala | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/src/engine/imap-db/imap-db-database.vala b/src/engine/imap-db/imap-db-database.vala
index 91e2f01c6..f1a5e323a 100644
--- a/src/engine/imap-db/imap-db-database.vala
+++ b/src/engine/imap-db/imap-db-database.vala
@@ -109,6 +109,8 @@ private class Geary.ImapDB.Database : Geary.Db.VersionedDatabase {
         if ((recommended & GC.RecommendedOperation.REAP) != 0) {
             // run in the background and allow application to continue running
             this.gc.reap_async.begin(gc_cancellable, on_reap_async_completed);
+        } else {
+            this.gc = null;
         }
 
         if (cancellable != null)