x11/wshowkeys: unbreak runtime after d81a61abe4
$ WAYLAND_DEBUG=1 wshowkeys
[...]
[0.182] -> wl_compositor@5.create_surface(new id wl_surface@3)
[0.185] -> zwlr_layer_shell_v1@7.get_layer_surface(new id zwlr_layer_surface_v1@11, wl_surface@3, nil, 2, "showkeys")
[0.192] -> zwlr_layer_surface_v1@11.set_anchor(0)
[0.194] -> zwlr_layer_surface_v1@11.set_margin(32, 32, 32, 32)
[0.198] -> zwlr_layer_surface_v1@11.set_exclusive_zone(-1)
[0.200] -> wl_surface@3.commit()
[0.296] -> wl_surface@3.attach(nil, 0, 0)
[0.302] -> wl_surface@3.commit()
[0.313] wl_display@1.error(zwlr_layer_surface_v1@11, 1, "width 0 requested without setting left and right anchors")
zwlr_layer_surface_v1@11: error 1: width 0 requested without setting left and right anchors
wl_display_dispatch: Protocol error
03855710ed