~/.config/dwm: Add stop after current song shortcut

.config/dwm/config.h

static const char *volumeupcmd[] = { "amixer", "set", "Master", "5%+", NULL };
static const char *volumetogglecmd[] = { "amixer", "set", "Master", "toggle", NULL };
static const char *musicplayercmd[] = { "quodlibet", NULL };
static const char *musicstopaftercmd[] = { "quodlibet", "--stop-after=t", NULL };
static const char *screenlockcmd[] = { "slock", NULL };
	{ MODKEY|ShiftMask,             XK_m,                    view,  {.ui = 1 << 4} },
	{ MODKEY|ShiftMask,             XK_m,                    spawn, { .v = musicplayercmd } },
	{ ShiftMask,                    XF86XK_AudioPlay,        spawn, { .v = musicstopaftercmd } },
	{ MODKEY|ShiftMask,             XK_l,      spawn,          { .v = screenlockcmd } },
};