Delete virtual parent folders

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

@@ -1766,7 +1766,9 @@ class Core {
         Log.i("Delete local count=" + local.size());
         for (String name : local.keySet()) {
             EntityFolder folder = local.get(name);
-            if (EntityFolder.USER.equals(folder.type)) {
+            List<EntityFolder> childs = parentFolders.get(name);
+            if (EntityFolder.USER.equals(folder.type) ||
+                    childs == null || childs.size() == 0) {
                 Log.i(name + " delete");
                 db.folder().deleteFolder(account.id, name);
             } else