Blender Git Loki

WM: return success from WM_recover_last_session, minor cleanup

- Return success from WM_recover_last_session
- Avoid setting global variables is already called in WM_file_read.
While it didn't cause any problems, these assignments ran even when
recovering the session failed to load the file.
- Return OPERATOR_CANCELLED when the operator fails.

Returning success is needed to fix T85011.