(track-changes--after): Fix problem found in bug#73041

(track-changes--after): Fix problem found in bug#73041

When calling `track-changes--before` (e.g. because of a missing
b-f-c or for some other reason), it sets `track-changes--before-end`
to the right value so we shouldn't increment it right after.
Also, we should update `track-changes--buffer-size` before
calling `track-changes--before` so it doesn't risk signaling
a spurious inconsistency.

* lisp/emacs-lisp/track-changes.el (track-changes--after):
Update `track-changes--buffer-size` earlier, and don't increment
`track-changes--before-end` when we call `track-changes--before`.