Blender Git Loki

Fix T93442: Crash when proxy building is cancelled

If strip is removed while proxy is built, this causes crash when
building is finished. This happens because proxy anims are freed in
`SEQ_proxy_rebuild_finish()`.

Iterate over available strips and check if original strip still exists
by comparing `SessionUUID`.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D13408