bug#37623: 27.0.50; describe-key fails in tab-bar-mode

[Juri Linkov <juri@linkov.net>]

>>> It appears as though describe-key fails when the mouse is pressed on a
>>> non-currently-active tab in the tab-bar:
>>>
>>> emacs -Q
>>> M-x tab-bar-mode
>>> C-x b RET
>>> C-h k (then click the mouse button on a non-currently-active tab):
>>>
>>> run-hook-with-args: Wrong type argument: symbolp, #[0 "ÁÀ!‡" [(tab
>>> (name . "*scratch*") (time . 1570198894) (wc . #<window-configuration>)
>>> (ws ((min-height . 4) (min-width . 10) (min-height-ignore . 2)
>>> (min-width-ignore . 6) (min-height-safe . 1) (min-width-safe . 2)
>>> (min-pixel-height . 68) (min-pixel-width . 80) (min-pixel-height-ignore
>>> . 34) (min-pixel-width-ignore . 48) ...) leaf (pixel-width . 1600)
>>> (pixel-height . 714) (total-width . 200) (total-height . 42)
>>> (normal-height . 1.0) (normal-width . 1.0) (buffer "*scratch*" (selected
>>> . t) (hscroll . 0) (fringes 8 8 nil nil) (margins nil) (scroll-bars nil
>>> 2 t nil 0 t nil) (vscroll . 0) (dedicated) (point . 146) ...)))
>>> tab-bar-select-tab] 2 nil nil]Cannot find image file
>>> ‘/build/source/etc/images/tabs/close.xpm’
>>
>> From what I see, you clicked the mouse button on the tab close button,
>> right?
>
> Anywhere in a non-active tab, not just on the tab close button.

I see that today Lars fixed this help-mode bug in f2cbc7214f, so
now it's possible to use lambdas in menu items.

Please try again.

> The message about the image file not being found is unrelated (probably,
> anyway), seems to be another bug or issue with my build. I get *tons*
> (thousands) of these messages but haven't had time to look into it yet:
>
> Cannot find image file ‘/build/source/etc/images/tabs/close.xpm’
> Cannot find image file ‘/build/source/etc/images/tabs/new.xpm’

I don't know why your build has no images, but I'll fix these warnings
by checking if the image exists.