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

[Alex Branham]

Hi, and thanks for all the work on tab-bar-mode!

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’

Thanks,
Alex

In GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.10)
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: NixOS 19.03.173553.6420e2649fa (Koi)

Configured using:
 'configure
 --prefix=/nix/store/79qhpwxjkiczd5zbhqlr183dq7340rwz-emacs-27.0.50
 --disable-build-details --with-modules --with-x-toolkit=gtk3 --with-xft
 CFLAGS=-DMAC_OS_X_VERSION_MAX_ALLOWED=101200'

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND DBUS GSETTINGS GLIB NOTIFY INOTIFY
LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD JSON
PDUMPER GMP

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Memory information:
((conses 16 738894 80787)
 (symbols 48 56491 67)
 (strings 32 210994 11090)
 (string-bytes 1 6887125)
 (vectors 16 112908)
 (vector-slots 8 2382739 96402)
 (floats 8 1127 347)
 (intervals 56 18313 1652)
 (buffers 1000 47))