Fix app shortcuts in fullscreen

[mgi]

Hi,

Here is a patch that I have for some times now into my init.el. It is based on a patch I found here: https://github.com/ch11ng/exwm/issues/786.

What does it fix?

When using an application that you can toggle to fullscreen (for instance mpv with f shortcut), you are not able to use any of the application shortcuts after that (even untoggling fullscreen). This patch fixes this.

Thanks.