[geary] Fix race destroying upgrade dialog when upgrade multiple accounts.

[Michael Gratton <mjog src gnome org>]

commit 2015760d092bb1292387b65253ea781c4dd5f00e
Author: Michael James Gratton <mike vee net>
Date:   Mon Aug 15 10:07:25 2016 +1000

    Fix race destroying upgrade dialog when upgrade multiple accounts.
    
    If one account DB upgrade completes before the next one starts, the
    upgrade will be destroyed and become invalid, leading to errors when the
    next does start.
    
    This fix keeps the dialog around permanently, which is a waste of RAM,
    but that's better than crashing.
    
    * src/client/dialogs/upgrade-dialog.vala (Object): Hide, don't destroy
      the upgrade dialog when it is hidden.

 src/client/dialogs/upgrade-dialog.vala |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/client/dialogs/upgrade-dialog.vala b/src/client/dialogs/upgrade-dialog.vala
index 9d0b782..3543f02 100644
--- a/src/client/dialogs/upgrade-dialog.vala
+++ b/src/client/dialogs/upgrade-dialog.vala
@@ -52,7 +52,7 @@ public class UpgradeDialog : Object {
         }
         
         if (dialog.visible)
-            dialog.destroy();
+            dialog.hide();
     }
     
     /**