[BUG] org-plot/gnuplot with dates in brackets does not work anymore [9.8-pre (release_9.7.6-97-g90d4ae @ /home/ck/.emacs.d/straight/build/org/)]

[Chris Keschnat]

Hello,
after e0924db3, =org-plot/gnuplot= does not work with dates in brackets anymore.
I am unsure if this syntax is supported, but it was working before.

Example table:

#+PLOT: title:"Daily Temperature Readings" ind:1 deps:(2) type:2d 
with:linespoints timeind:1
| Date         | Temperature (°C) |
|--------------+------------------|
| [2024-07-24] |             28.5 |
| [2024-07-25] |             29.2 |
| [2024-07-26] |             27.8 |
| [2024-07-27] |             30.1 |
| [2024-07-28] |             31.3 |
| [2024-07-29] |             29.7 |
| [2024-07-30] |             28.9 |

~C-c C-c~ on the PLOT line results in:
#+begin_src conf
  Debugger entered--Lisp error: (wrong-type-argument stringp nil)
    format-time-string(nil (26272 10208))
    org-plot-quote-timestamp-field("[2024-07-24 Wed]")
    org-plot-quote-tsv-field("[2024-07-24 Wed]")
    funcall(org-plot-quote-tsv-field "[2024-07-24 Wed]")
    (setq contents (funcall 'org-plot-quote-tsv-field contents))
    (cond nil (t (setq contents (funcall 'org-plot-quote-tsv-field contents))))
    (progn nil (cond nil (t (setq contents (funcall 'org-plot-quote-tsv-field 
contents)))))
    (if contents (progn nil (cond nil (t (setq contents (funcall 
'org-plot-quote-tsv-field contents))))))
    (when contents nil (cond nil (t (setq contents (funcall 
'org-plot-quote-tsv-field contents)))))
  <cut>
#+end_src

Thank you


Emacs  : GNU Emacs 29.4 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.41, 
cairo version 1.18.0)
Package: Org mode version 9.8-pre (release_9.7.6-97-g90d4ae @ 
/home/ck/.emacs.d/straight/build/org/)