Fix failure to decrypt first message to self after key change

The problem was in the handle_fingerprint_change() function which
attempted to add a warning about fingerprint change to all chats with
the contact.

This failed because of the SQL query failing to find the contact for
self in the `contacts` table. So the warning was not added, but at the
same time the whole decryption process failed.

The fix is to skip handle_fingerprint_change() for self addreses.

src/peerstate.rs

@@ -267,6 +267,11 @@ impl Peerstate {
         context: &Context,
         timestamp: i64,
     ) -> Result<()> {
+        if context.is_self_addr(&self.addr).await? {
+            // Do not try to search all the chats with self.
+            return Ok(());
+        }
+
         if self.fingerprint_changed {
             if let Some(contact_id) = context
                 .sql