fix(electron): crash when cancelling screen picker

Calling callback({}) with an empty object caused Electron to throw
"Video was requested, but no video stream was provided". The correct
way to cancel/deny the request is callback() with no arguments.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

electron/main.js

@@ -134,7 +134,7 @@ function createWindow() {
   session.defaultSession.setDisplayMediaRequestHandler(async (_request, callback) => {
     const sources = await desktopCapturer.getSources({ types: ['screen', 'window'], thumbnailSize: { width: 320, height: 180 } });
     if (sources.length === 0) {
-      callback({});
+      callback();
       return;
     }
 
@@ -232,7 +232,7 @@ document.getElementById('cancelBtn').addEventListener('click', () => {
       try { fs.unlinkSync(tmpFile); } catch {}
 
       if (!selection) {
-        callback({});
+        callback();
         return;
       }
       const selectedId = typeof selection === 'string' ? selection : selection.id;
@@ -241,7 +241,7 @@ document.getElementById('cancelBtn').addEventListener('click', () => {
       if (chosen) {
         callback(withAudio ? { video: chosen, audio: 'loopback' } : { video: chosen });
       } else {
-        callback({});
+        callback();
       }
     };
 
@@ -252,7 +252,7 @@ document.getElementById('cancelBtn').addEventListener('click', () => {
       if (!resolved) {
         resolved = true;
         ipcMain.removeListener(PICKER_CHANNEL, onPickerResult);
-        callback({});
+        callback();
       }
     });
   });