Can't index `supported_loaders` when calling `add_loader` interface during `on_load`

[kirazy]

Error message or bug description

Error while running event vanilla-loaders-hd::on_load()
Error when running interface function loader-redux.add_loader: LoaderRedux/control.lua:26: attempt to index field 'supported_loaders' (a nil value)
stack traceback:
LoaderRedux/control.lua:26: in function <LoaderRedux/control.lua:24>
stack traceback:
[C]: in function 'call'
vanilla-loaders-hd/control.lua:209: in function 'do_init'
vanilla-loaders-hd/control.lua:231: in function <vanilla-loaders-hd/control.lua:230>

Relevant lines from vanilla-loaders-hd:
https://github.com/kirazy/vanilla-loaders-hd/blob/master/control.lua#L206-L232

To Reproduce
https://mods.factorio.com/mod/vanilla-loaders-hd/discussion/623f6acfb620f1c4a1edc98e

I've asked him to upload a save. I'm expecting this is related to changes for #53, commit 7ada2b7. I can't personally reproduce this issue and a quick examination of control.lua doesn't expose anything obvious to me.

Loader Redux version
1.7.2

[0ptera]

Loader tables where made global to be MP save.
With this using add_loader and remove_loader in on_load is no longer possible.
Please use on_init and on_configuration_changed instead.