bug#37385: 27.0.50; Crash on multibyte assertion violation

[Juri Linkov <juri@linkov.net>]

>> I tried the following fix and it prevents the crash:
>
> Thanks, but this is a backward-incompatible change on too low a level.
> It is a long-standing "convention" in Emacs that Lisp strings rendered
> as part of, or in relation to, unibyte buffers are assumed unibyte by
> default, and I don't want to change that -- who knows how many places
> in the code rely on this implicit assumption?
>
> Also, the change in reseat_1 looks unnecessary, as I'd be surprised if
> that function was called in your use case (reseat_1 is used only when
> displaying buffers, not strings).
>
> Please try an alternative patch below.  (I don't have access to an X
> build without a toolkit, so I cannot test this myself.)

Thanks for the proper fix.  I tried and it works without problems.
Also I found third place (in addition to two places in your patch)
where STRING_MULTIBYTE could be used for reseat_to_string.  Is the
following change needed as well?

diff --git a/src/xdisp.c b/src/xdisp.c
index 9f999c7903..af6faf9d34 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -13804,7 +13812,8 @@ tool_bar_height (struct frame *f, int *n_rows, bool pixelwise)
   temp_row->reversed_p = false;
   it.first_visible_x = 0;
   it.last_visible_x = WINDOW_PIXEL_WIDTH (w);
-  reseat_to_string (&it, NULL, f->desired_tool_bar_string, 0, 0, 0, -1);
+  reseat_to_string (&it, NULL, f->desired_tool_bar_string,
+                    0, 0, 0, STRING_MULTIBYTE (f->desired_tool_bar_string));
   it.paragraph_embedding = L2R;
 
   while (!ITERATOR_AT_END_P (&it))