Fix drm::control::Device::add_planar_buffer when GBM Bo uses DrmModifier::Invalid

[tronical]

When adding a GBM supplied buffer via add_planar_buffer, since commit 6cb3a27d5b3f4fecb5415bed69497491759126a9 the modifiers are fetched directly from the planar buffer trait. What the code does not take into account though is when the GBM bo returns DrmModifier::Invalid. In that case add_fb2 expects 0 as modifier in the array for each plane, instead of DRM_FORMAT_MOD_INVALID.

[tronical]

One could argue that the PlanarBuffer implementation of BufferObject in gbm, fn modifiers(&self) -> Option<Modifier> should return None for DrmModifier::Invalid. I can make a PR for that - separately - but meanwhile I think since the ::Invalid variant does exist, it makes sense to "support" it.

[tronical]

I force-pushed to get the formatting fixed (my bad).

[tronical]

The CI failure looks bogus. The error about the invalid cast looks like it was from a build of an earlier sha. The latest build in https://github.com/Smithay/drm-rs/actions/runs/8346623741 has only the (seemingly unrelated) drm_syncobj failures.

[Drakulix]

Could you rebase? https://github.com/Smithay/drm-rs/pull/190 should have fixed CI.

[tronical]

Done :)

[Drakulix]

Thanks!