Since repeaters have no value by themselves, a repeater that contains only another repeater was throwing a "widget not bound to controller" exception when adding a new item - the repeater item processing was not creating a form widget for the inner repeater on load, or in an AJAX call. This fix specifically checks if a child repeater has called for a new item, and if so and the current repeater has no value for this particular item, it will add a "stub" form widget to correctly bind the widget.
Fixes#4344.
b5a3c64bf1