bug#57476: 29.0.50; Mouse wheel event ignored on Lucid build

[Stephen Berman <stephen.berman@gmx.net>]

0. emacs -Q
1. Display a buffer with enough lines to scroll, e.g.:
   C-x d /path/to/emacs/sources RET
2. Scroll mouse wheel
=> The buffers fails to scroll.
3. Type `C-h k' and then scroll the mouse wheel
=> The echo area shows no input, only the prompt "Describe the following
   key, mouse click, or menu item: "

I see this only on the Lucid build.  Also on Lucis, if I hold down
mouse-1 or mouse-3 and simultaneously scroll the wheel, then the buffer
does scroll.  After releasing mouse-1 or mouse-3, scrolling the wheel
scrolls the buffer once by one line (either up or down).  Further
scrolling of the wheel fails to scroll the buffer.


In GNU Emacs 29.0.50 (build 2, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.17.6, Xaw scroll bars) of 2022-08-28 built on strobelfs2
Repository revision: 35af917f187719fecadde278a51fd10bf47eed07
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101004
System Description: Linux From Scratch r11.0-165

Configured using:
 'configure -C --with-x-toolkit=lucid --with-xinput2 'CFLAGS=-Og -g3''

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBSYSTEMD LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG RSVG
SECCOMP SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS WEBP X11 XDBE XIM
XINPUT2 XPM LUCID ZLIB