bug#54656: 29.0.50; [menu] key is not read anymore

[dal-blazej]

> I guess what you have to do is to step through each statement until you
> find out why it isn't reaching this piece of handle_one_xevent:

It seems the key is ... initialized to 0 ?

(gdb) p xkey
$13 = {type = 0, serial = 0, send_event = 1466608144,
  display = 0x898f22a9e227e100, window = 140737488343872, root = 93824994679155,
  subwindow = 0, time = 93824993826130, x = 2, y = 0, x_root = 0, y_root = 0,
  state = 0, keycode = 0, same_screen = 0}

(gdb) s

(gdb) p xkey.state
$14 = 0

(gdb) s
x_emacs_to_x_modifiers (dpyinfo=0x555557727a00, state=0) at lisp.h:1155

(gdb) p a
$15 = {i = {0, 1045149306}, d = 1.2904777690891933e-08}

(gdb) s
Fget (symbol=0x0, propname=0xaf80) at lisp.h:747

[...]

(gdb) u
x_emacs_to_x_modifiers (dpyinfo=0x555557727a00, state=0) at xterm.c:9546

(gdb) p tem
$21 = (Lisp_Object) 0x0

[...]

(gdb) n
handle_one_xevent (dpyinfo=0x555557727a00, event=0x7fffffffd5e0,
    finish=0x555555beabb8 <current_finish>, hold_quit=0x7fffffffd850)
    at xterm.c:13926

(gdb) p xkey.state
$30 = 0

At some point gdb prints
(gpb) n
0x00007ffff760623f in ?? () from /lib/x86_64-linux-gnu/libgdk-3.so.0

and I am unable to continue my inspection.