GX keyboard_string fix

Like the title says, a (hopefully temporary) fix for keyboard_string in the WASM/GX.Games export. This won't work on GX.Games when uploaded directly through the IDE, but it should work fine when exporting a WASM game as a zip. If you upload this zip file to GX Games, that should work.

https://github.com/Sidorakh/gx-keyboard-string