c2e31513b8
With the aim of removing `seqbasep` to remove the complicated logic for repairing pointers within the `Strip` struct when loading files and undo steps, this commit just moves access of the variable behind a function. In the future the function will retrieve the list from a Strip pointer, for now it just returns the existing pointer. Overall motivation is that blend file pointer manipulation is incompatible with the changes required for #127706. Pull Request: https://projects.blender.org/blender/blender/pulls/144624