Fixed thread with empty msgid

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

@@ -1533,7 +1533,8 @@ public class MessageHelper {
         DB db = DB.getInstance(context);
 
         List<String> all = new ArrayList<>(refs);
-        all.add(msgid);
+        if (!TextUtils.isEmpty(msgid))
+            all.add(msgid);
 
         int thread_range = prefs.getInt("thread_range", MessageHelper.DEFAULT_THREAD_RANGE);
         int range = (int) Math.pow(2, thread_range);

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

@@ -36,6 +36,6 @@ public class TupleThreadInfo {
     }
 
     public boolean isReferencing(String msgid) {
-        return !isSelf(msgid) && !isReferenced(msgid);
+        return !TextUtils.isEmpty(msgid) && !isSelf(msgid) && !isReferenced(msgid);
     }
 }