bug#42887: 28.0.50; Customize Group doesn't show/hide option on repeated clicking

[Stefan Kangas]

Clicking with the mouse to show/hide the options in a custimize group
doesn't handle repeated clicks well.  Steps to reproduce:

0. emacs -Q
1. M-x customize-group RET mouse RET
2. Click the arrow next to an option to expand it
3. [wait a second without moving the mouse cursor]
4. Click again

Result: the option does not expand

Expected result: the option expands


In GNU Emacs 28.0.50 (build 3, x86_64-pc-linux-gnu, GTK+ Version
3.24.20, cairo version 1.16.0)
 of 2020-08-10 built on joffe
Repository revision: 52418648a47b48538c998b1b0a3be8110fff3fdf
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Debian GNU/Linux bullseye/sid

Configured using:
 'configure --enable-checking=yes,glyphs --enable-check-lisp-object-type
 'CFLAGS=-O0 -g3'
 
PKG_CONFIG_PATH=/home/skangas/usr/lib/pkgconfig:/home/skangas/usr/lib/pkgconfig:'

Configured features:
XPM JPEG TIFF GIF PNG RSVG CAIRO SOUND GPM DBUS GSETTINGS GLIB NOTIFY
INOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF
ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD
JSON PDUMPER LCMS2