bug#60297: 30.0.50; tab-bar-mode does not resize tabs without close button

[Juri Linkov]

close 60297 30.0.50
thanks

> The 'tab-bar-mode' can shrink tabs that exceed a certain width (see
> 'tab-bar-auto-width' and related).  This does not work when
> 'tab-bar-close-button-show' is set to nil.
>
> In the scratch buffer of 'emacs -Q':
>
> - Evaluate (tab-bar-mode 1)
>
> - The tab shows the name of the buffer.
>
> - Now rename the buffer to something long:
>   (rename-buffer "This is a very long title just to test if tabs have a max 
> width as expected.")
>
> - The tab does not grow as much as the new name.
>
> - Now disable the close button: (setq tab-bar-close-button-show nil)
>
> - Evaluate again (tab-bar-mode 1)
>
> - The tab is not responding to 'tab-bar-auto-width'.

Thanks for the bug report.  This broke in 30.0.50 after replacing 'setf'
with code from 'cl--set-substring' in the commit 9452dc4821a.
Now this is fixed by copying more logic from 'cl--set-substring'.