Fixed delete unseen option

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

@@ -3937,7 +3937,8 @@ class Core {
             cal_keep.set(Calendar.MILLISECOND, 0);
 
             Calendar cal_keep_unread = Calendar.getInstance();
-            cal_keep_unread.add(Calendar.DAY_OF_MONTH, -Math.max(keep_days * 6, EntityFolder.DEFAULT_KEEP * 6));
+            cal_keep_unread.add(Calendar.DAY_OF_MONTH,
+                    delete_unseen ? keep_days * 6 : -Math.max(keep_days * 6, EntityFolder.DEFAULT_KEEP * 6));
             cal_keep_unread.set(Calendar.HOUR_OF_DAY, 0);
             cal_keep_unread.set(Calendar.MINUTE, 0);
             cal_keep_unread.set(Calendar.SECOND, 0);