label_format does not see Generic Chooser

[rgs258]

It looks like that when a ChooserBlock (or subclass) is within a StructBlock, the selected object's label is not able to contribute to getTextLabel (I think?) and so the next block is looked to for the StructBlock's label. When a ChooserBlock is specified explicitly in label_format, then null is given as the name in the editor. Seems like somehow getTextLabel just needs to see the result of get_title on the AdminChooser. ...I'd try to get you a PR, but I just don't have the time to go any deeper. Very much appreciate all the work you put into this!