bug#55579: 29.0.50; Abbrevs not saved on exit anymore

[Juri Linkov]

After a recent change, 'C-x C-c' doesn't ask anymore to save abbrevs with:

  Save abbrevs in ~/.emacs.d/abbrev_defs?

It looks like the regression was caused by ce220524fcf.
Before this change, save-buffers-kill-emacs unconditionally
called save-some-buffers that also saves the abbrev table.
But after the change, save-some-buffers that saves abbrevs
is called only when files--buffers-needing-to-be-saved
detects unsaved buffers.