Fix/Add basic unicode support in the console

Actually, you can't type "non-ascii" characters in the console (on linux), with this patch the same workaround used here ( https://github.com/minetest/minetest/commit/b24b8de00b7ab5f81b0e0255509af3f10f6e2514#L16R276 ), is used for the console.

edit: this is only valid for linux