Default value must be lowercase for mixed case delta

In the issue #1182432: Block delta can be mixed upper- and lowercase you wrapped the delta in a drupal_strtolower function to be compatible with jquery on lowercase classes. This is correct, but when checking for a default value in the form alter, you check for the delta in the settings array without setting it to lower class.

This means that if a delta is mixed case, the form will not find a default value for it.

I suggest putting the same drupal_strtolower function around the delta when finding the default value.