multigpu: Fix storing of copied textures.
multigpu: Fix storing of copied textures.

Previously we were accidentally storing an `Option<TextureType>`
instead of a `TextureType` inside our AnyMap, resulting in being
unable to retrieve the textures later as the types didn't match up.

This commit fixes this and just stores nothing in case of an error.

Smithay/smithay,Smithay/smithay,Smithay/smithay,Smithay/smithay