mask manager: fix use-after-free when selecting a group

[da-phil]

Tree rows keep raw dt_iop_module_t pointers, but modules are freed on image change and on darkroom leave. The structure-hash early-out in gui_update can keep a store built for the previous set of modules, so selecting a group row called flags() through a dangling pointer and segfaulted.

Drop dead modules in _lib_masks_get_values() and invalidate the cached tree hash on image change and darkroom entry.

Fixes: #21852

Disclaimer: this work has been co-created with Claude.

[hats-np]

No such luck. Unsure if it's related to this, but it keeps segfaulting. Now when opening the quick access panel. Seems to not be related to this PR.
darktable_bt_HUAIU3.txt

[hats-np]

It's not related to this. I will test it again after I can use dt properly...

[da-phil]

No such luck. Unsure if it's related to this, but it keeps segfaulting. Now when opening the quick access panel. Seems to not be related to this PR. darktable_bt_HUAIU3.txt

Thanks for checking, will have another look in the meantime...

[TurboGit]

@da-phil : I'm a bit reluctant to merge this as we have the full revamp of mask support by @masterpiga, so probably better wait for it to land in Darktable and avoid conflicts.

[da-phil]

@da-phil : I'm a bit reluctant to merge this as we have the full revamp of mask support by @masterpiga, so probably better wait for it to land in Darktable and avoid conflicts.

No worries, this PR was also meant to fix a bug which it didn't. I need to keep investigating.