fix: ignore special chats when calculating similar chats

The second SQL statement calculating chat size
was already fixed in f656cb29be,
but more important statement calculating member list intersection
was overlooked.
As a result, trash chat with members added there due to former bugs
could still appear in similar chats.

src/chat.rs

@@ -993,8 +993,9 @@ impl ChatId {
                    AND y.contact_id > 9
                    AND x.chat_id=?
                    AND y.chat_id<>x.chat_id
+                   AND y.chat_id>?
                  GROUP BY y.chat_id",
-                (self,),
+                (self, DC_CHAT_ID_LAST_SPECIAL),
                 |row| {
                     let chat_id: ChatId = row.get(0)?;
                     let intersection: f64 = row.get(1)?;