Auto link broken threads

app/src/main/java/eu/faircode/email/DaoMessage.java

@@ -587,6 +587,9 @@ public interface DaoMessage {
     @Query("UPDATE message SET revisions = :revisions WHERE id = :id")
     int setMessageRevisions(long id, Integer revisions);
 
+    @Query("UPDATE message SET thread = :thread WHERE id = :id")
+    int setMessageThread(long id, String thread);
+
     @Query("UPDATE message" +
             " SET content = 0, fts = 0, language = NULL, plain_only = NULL, preview = NULL" +
             " WHERE id = :id")

app/src/main/java/eu/faircode/email/MessageHelper.java

@@ -873,12 +873,19 @@ public class MessageHelper {
         if (!TextUtils.isEmpty(inreplyto) && !refs.contains(inreplyto))
             refs.add(inreplyto);
 
+        String thread = null;
         DB db = DB.getInstance(context);
         for (String ref : refs) {
             List<EntityMessage> messages = db.message().getMessagesByMsgId(account, ref);
-            if (messages.size() > 0)
-                return messages.get(0).thread;
+            for (EntityMessage message : messages) {
+                if (thread == null)
+                    thread = message.thread;
+                if (thread != null && !thread.equals(message.thread))
+                    db.message().setMessageThread(message.id, thread);
+            }
         }
+        if (thread != null)
+            return thread;
 
         if (refs.size() > 0)
             return refs.get(0);