this corrects the To:-list for group-messages with only SELF as member.

before, the list was empty
and trying to send to groups that only contain SELF lead to a crash.

in theory, this happens for both, bcc_self enabled or not, however,
if bcc_self was disabled (default setting),
things worked as the whole mimerendering was skipped on a higher level.
also, the saved-messages-chat was not affected as this was checked explicitly.

this pr changes the mimerendering so that From: is used as To:
if there is no recipient-list and the messasge will be sent to SELF only.

src/mimefactory.rs

@@ -368,7 +368,7 @@ impl<'a, 'b> MimeFactory<'a, 'b> {
             self.from_addr.clone(),
         );
 
-        let mut to = Vec::with_capacity(self.recipients.len());
+        let mut to = Vec::new();
         for (name, addr) in self.recipients.iter() {
             if name.is_empty() {
                 to.push(Address::new_mailbox(addr.clone()));
@@ -380,6 +380,10 @@ impl<'a, 'b> MimeFactory<'a, 'b> {
             }
         }
 
+        if to.is_empty() {
+            to.push(from.clone());
+        }
+
         if !self.references.is_empty() {
             unprotected_headers.push(Header::new("References".into(), self.references.clone()));
         }