FIX: fix/improve sanitize collection functionality

As I've started using cl-naive-store I've noticed that sanitize collection is not working as expected for me. When I call sanitize-data-file on collection it either cleared my .log file completely (as it was not actually writing to the .new file due to relying on location slot instead of on file name) or it was throwing an exception when the file with .new extention did not yet exist. This pr makes sanitize-data-file to always write current 'sanitized' collection to the .new file before copying it to the .log file.

If I understood Your documentation, code and intentions correctly this merge request could be considered an improvement.

NOTE: This is my first ever merge request to Common Lisp project and I admit to beeing a newbie in CL land, so please be understanding :) I'm trying to gain/improve CL skills by working on a private project which I and my team are currently using as internal tool in my contract job.