fix(midi): ensure midin initializes device state correctly

The midin function only initialized the refs object for a device on the initial MIDI setup. This caused an error if a second MIDI device was connected in the same session, as its refs object would not exist, leading to a 'cannot read properties of undefined' error when accessed.

This commit fixes the issue by ensuring that the refs object for a given MIDI input is initialized every time  is called, not just on the first call.

packages/midi/midi.mjs

@@ -493,6 +493,9 @@ export async function midin(input) {
         otherInputs?.length ? `Also available: ${getMidiDeviceNamesString(otherInputs)}` : ''
       }`,
     );
+  }
+  // ensure refs for this input are initialized
+  if (!refs[input]) {
     refs[input] = {};
   }
   const cc = (cc) => ref(() => refs[input][cc] || 0);