Crash enumerating inputs on Web

[RuiVarela]

Hi, thanks for the great lib,

I've spotted a crash while trying to enumerate inputs on emscripten,

        libremidi::observer obs;
        for(libremidi::input_port const& port : obs.get_input_ports()) {
...
        }

Uncaught TypeError: Cannot read properties of undefined (reading 'inputs')
    at 26701691 (DropThatBeat.js:9812:102)
    at runEmAsmFunction (DropThatBeat.js:4163:30)
    at _emscripten_asm_const_int (DropThatBeat.js:4166:14)
    at DropThatBeat.wasm.libremidi::webmidi_helpers::midi_access_emscripten::load_current_infos(web_build/) (http://localhost:8080/web_build/DropThatBeat.wasm)
    at DropThatBeat.wasm.libremidi::observer_emscripten::get_input_ports(web_build/) const (http://localhost:8080/web_build/DropThatBeat.wasm)
    at DropThatBeat.wasm.libremidi::observer::get_input_ports(web_build/) const (http://localhost:8080/web_build/DropThatBeat.wasm)

which points to

26701691: () => { let inputs = []; let outputs = []; for (let inpt of globalThis.__libreMidi_access.inputs.values()) { inputs.push(inpt); } ....

I'm using emsdk 4.0.10 and libremidi 5.3.1