bug#73050: 30.0.90; Empty tool tip when hovering over tab-bar separator

[Juri Linkov <juri@linkov.net>]

>> >> Maybe this unasked-for default fallback is not needed after all:
>> >>
>> >> diff --git a/src/xdisp.c b/src/xdisp.c
>> >> index f9a10267bad..18834c6b781 100644
>> >> --- a/src/xdisp.c
>> >> +++ b/src/xdisp.c
>> >> @@ -15155,8 +15155,6 @@ note_tab_bar_highlight (struct frame *f, int x, int y)
>> >>    help_echo_object = help_echo_window = Qnil;
>> >>    help_echo_pos = -1;
>> >>    help_echo_string = AREF (f->tab_bar_items, prop_idx + TAB_BAR_ITEM_HELP);
>> >> -  if (NILP (help_echo_string))
>> >> -    help_echo_string = AREF (f->tab_bar_items, prop_idx + TAB_BAR_ITEM_CAPTION);
>> >>  }
>> >>
>> >>  #endif /* HAVE_WINDOW_SYSTEM */
>> >
>> > Do you remember why was this introduced?
>> 
>> It was copy-pasted from tool-bar code.
>
> But on the tool bar there are no empty space between buttons.  On the
> tab bar, there is.  What I don't understand is why those empty spaces
> have tooltips.  Because each tab-bar button has a valid, non-nil
> tooltip, so the problem is with the tooltips popped up when the mouse
> is between buttons.  Do you understand why this happens?

When there is no TAB_BAR_ITEM_HELP, then it falls back to TAB_BAR_ITEM_CAPTION.
But the tab bar doesn't need tooltips on spaces.  So this patch is needed.