Fix behaviour change in error handling, introduced by commit f284fb71dda0ea9754f1582c6951d5f462e947bc

As pointed out on https://github.com/inverse-inc/sogo/pull/201#discussion_r54881994

UI/MailerUI/UIxMailEditor.m

@@ -869,7 +869,7 @@ static NSArray *infoKeys = nil;
     {
       error = [self validateForSend];
       if (!error)
-        error = [co sendMailAndCopyToSent: false];
+        error = [co sendMailAndCopyToSent: YES];
       else
 	error = [self failedToSaveFormResponse: [error reason]];
     }