bug#36900: key-mon crashes on launch

[Alexandros Theodotou <alex@zrythm.org>]

Hi Tobias,

On Sun, 2021-01-03 at 22:58 +0100, Tobias Geerinckx-Rice wrote:
> guix environment key-mon --ad-hoc key-mon -- key-mon


I tried the command above and this is my output.
```
substitute: updating substitutes from 'https://ci.guix.gnu.org'...
100.0%
1.7 MB will be downloaded
downloading from 
https://ci.guix.gnu.org/nar/lzip/kffsg08xjyzvxddldyqc2xfhiflsk0y6-python2-pygtk-2.24.0-doc
...
 python2-pygtk-2.24.0-
doc  776KiB                                                            
                                                                       
                                1.4MiB/s 00:01 [##################]
100.0%

The following derivation will be built:
   /gnu/store/mxpnh35lkla14p5f8al3s6vl2sh2w0cd-profile.drv

applying 16 grafts for /gnu/store/p35rw37wg8za9ygwv2q24lcg6a855rw4-
python2-pygtk-2.24.0.drv ...
building CA certificate bundle...
building fonts directory...
generating GLib schema cache...
creating GTK+ icon theme cache...
building cache files for GTK+ input methods...
building directory of Info manuals...
building database for manual pages...
building XDG desktop file cache...
building XDG MIME database...
building profile with 60 packages...

(.key-mon-real:15064): Gtk-WARNING **: 22:14:36.432: Unable to locate
theme engine in module_path: "adwaita",

(.key-mon-real:15064): Gtk-WARNING **: 22:14:36.434: Unable to locate
theme engine in module_path: "murrine",

(.key-mon-real:15064): Gtk-WARNING **: 22:14:36.434: Unable to locate
theme engine in module_path: "murrine",

(.key-mon-real:15064): Gtk-WARNING **: 22:14:36.434: Unable to locate
theme engine in module_path: "murrine",

(.key-mon-real:15064): Gtk-WARNING **: 22:14:36.435: Unable to locate
theme engine in module_path: "murrine",

(.key-mon-real:15064): Gtk-WARNING **: 22:14:36.435: Unable to locate
theme engine in module_path: "murrine",

(.key-mon-real:15064): Gtk-WARNING **: 22:14:36.435: Unable to locate
theme engine in module_path: "murrine",

(.key-mon-real:15064): Gtk-WARNING **: 22:14:36.435: Unable to locate
theme engine in module_path: "murrine",
Traceback (most recent call last):
  File "/gnu/store/fwmb620wk7hadj0iqh8xrxs8a74xhw50-key-mon-
1.17/bin/.key-mon-real", line 3, in <module>
    km.main()
  File "/gnu/store/fwmb620wk7hadj0iqh8xrxs8a74xhw50-key-mon-
1.17/lib/python2.7/site-packages/keymon/key_mon.py", line 1032, in main
    keymon = KeyMon(opts)
  File "/gnu/store/fwmb620wk7hadj0iqh8xrxs8a74xhw50-key-mon-
1.17/lib/python2.7/site-packages/keymon/key_mon.py", line 130, in
__init__
    self.devices = xlib.XEvents()
  File "/gnu/store/fwmb620wk7hadj0iqh8xrxs8a74xhw50-key-mon-
1.17/lib/python2.7/site-packages/keymon/xlib.py", line 80, in __init__
    self.record_display = display.Display()
  File "/gnu/store/ccnd7dx7c1g64mrdhml7vg8qmf65fd67-python2-xlib-
0.27/lib/python2.7/site-packages/Xlib/display.py", line 89, in __init__
    self.display = _BaseDisplay(display)
  File "/gnu/store/ccnd7dx7c1g64mrdhml7vg8qmf65fd67-python2-xlib-
0.27/lib/python2.7/site-packages/Xlib/display.py", line 71, in __init__
    protocol_display.Display.__init__(self, *args, **keys)
  File "/gnu/store/ccnd7dx7c1g64mrdhml7vg8qmf65fd67-python2-xlib-
0.27/lib/python2.7/site-packages/Xlib/protocol/display.py", line 166,
in __init__
    raise error.DisplayConnectionError(self.display_name, r.reason)
Xlib.error.DisplayConnectionError: Can't connect to display ":1": No
protocol specified
```

I get the same error when i launch it as `key-mon` from the console,
after I installed the package.

I tried with `--pure` now and I get your error:
```
No protocol specified
/gnu/store/mzwxwalqni35m1m37xb5qvd0mv1g3sp9-python2-pygtk-
2.24.0/lib/python2.7/site-packages/gtk-2.0/gtk/__init__.py:57:
GtkWarning: could not open display
  warnings.warn(str(e), _gtk.Warning)
Error: Missing xlib, run sudo apt-get install python-xlib
```

> $ sudo apt-get install python-xlib
>  sudo: apt-get: command not found

Lol.

Thanks,
Alex