oc-mail: Return right change key after saving a draft mail

After saving a draft mail (this is done automatically by Outlook)
a GetProps call is done checking the PidTagChangeKey has been
updated properly. Without this patch, it returned MAPI_E_NOT_FOUND.

With this patch, we addressed that problem and we have updated
the Predecessor Change List metadata for the draft mail with the
change key provided by the client to avoid conflicting messages
whenever it is possible.

OpenChange/MAPIStoreMailFolder.m

@@ -999,6 +999,44 @@ _compareFetchResultsByMODSEQ (id entry1, id entry2, void *data)
   [versionsMessage save];
 }
 
+- (BOOL) updatePredecessorChangeListWith: (NSData *) changeKey
+                       forMessageWithKey: (NSString *) messageKey
+{
+  /* Update predecessor change list property given the change key. It
+     returns if the change key has been added to the list or not */
+  BOOL added = NO;
+  NSData *globCnt, *oldGlobCnt;
+  NSDictionary *messageEntry;
+  NSMutableDictionary *changeList;
+  NSString *guid;
+  struct XID *xid;
+
+  xid = [changeKey asXIDInMemCtx: NULL];
+  guid = [NSString stringWithGUID: &xid->NameSpaceGuid];
+  globCnt = [NSData dataWithBytes: xid->LocalId.data length: xid->LocalId.length];
+  talloc_free (xid);
+
+  messageEntry = [self _messageEntryFromMessageKey: messageKey];
+  if (messageEntry)
+    {
+      changeList = [messageEntry objectForKey: @"PredecessorChangeList"];
+      if (changeList)
+        {
+          oldGlobCnt = [changeList objectForKey: guid];
+          if (!oldGlobCnt || ([globCnt compare: oldGlobCnt] == NSOrderedDescending))
+            {
+              [changeList setObject: globCnt forKey: guid];
+              [versionsMessage save];
+              added = YES;
+            }
+        }
+      else
+        [self errorWithFormat: @"Missing predecessor change list to update"];
+    }
+
+  return added;
+}
+
 - (NSData *) changeKeyForMessageWithKey: (NSString *) messageKey
 {
   NSDictionary *messages, *changeKeyDict;