[geary/wip/721828-undo] Make revoke button insensitive as soon as started

[Jim Nelson <jnelson src gnome org>]

commit d782571866068aed0ab4bc70717731d78c0d2170
Author: Jim Nelson <jim yorba org>
Date:   Fri Jan 2 17:03:42 2015 -0800

    Make revoke button insensitive as soon as started

 .../imap-engine/imap-engine-revokable-move.vala    |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)
---
diff --git a/src/engine/imap-engine/imap-engine-revokable-move.vala 
b/src/engine/imap-engine/imap-engine-revokable-move.vala
index d1a58ee..52cb45b 100644
--- a/src/engine/imap-engine/imap-engine-revokable-move.vala
+++ b/src/engine/imap-engine/imap-engine-revokable-move.vala
@@ -43,6 +43,10 @@ private class Geary.ImapEngine.RevokableMove : Revokable {
     }
     
     private async bool internal_revoke_async(Cancellable? cancellable) throws Error {
+        // at this point, it's a one-shot deal: any error from here on out, or success, revoke
+        // is completed
+        can_revoke = false;
+        
         // moving from original destination to original source
         MinimalFolder? dest_folder = null;
         try {
@@ -53,16 +57,15 @@ private class Geary.ImapEngine.RevokableMove : Revokable {
         }
         
         if (dest_folder == null)
-            return can_revoke = false;
+            return can_revoke;
         
         // open, revoke, close, ensuring the close and signal disconnect are performed in all cases
         try {
             yield dest_folder.open_async(Geary.Folder.OpenFlags.NONE, cancellable);
             
             // watch out for messages detected as gone when folder is opened
-            if (can_revoke) {
+            if (destination_ids.size > 0) {
                 yield dest_folder.revoke_move_async(destination_ids, original_source, cancellable);
-                can_revoke = false;
                 
                 // there's not a super-reliable way to wait until the delete of the message in this
                 // folder has completed; could wait for the UID to be reported deleted, but it's