v1.21.14

Fix a minor regression when the title contains only sort-tag characters

This release fixes a minor regression introduced with Tp-Note v1.21.10: Note
files, created with title fields containing only sort tag characters, need an
`extra_separator` between in the sort-tag and the title in their filename.
Failing this rule caused cyclic filename change when synchronizing the note's
metadata and the filename. Now, an extra-separator is correctly inserted
as before.