Spaces integration causes errors after cache clear inside a space

This produces 2 errors (repeated for each box being loaded:

Notice: Undefined property: stdClass::$plugin_key in boxes_boxes_box_load_alter() (line 754 of ... boxes.module).
Notice: Undefined property: stdClass::$delta in boxes_box_load() (line 380 of ... boxes.module).

These basically occur because of an error in the boxes_box_load function:

The $delta is passed instead of $box->delta when the $delta from params is empty, thus the alter gets a null delta and loads all the boxes instead of just one.

Patch incoming.