Force quit mpv on app close (#4)

src/main/main.ts

@@ -165,6 +165,10 @@ export const getMainWindow = () => {
   return mainWindow;
 };
 
+app.on('before-quit', () => {
+  mainWindow?.webContents.send('renderer-player-quit');
+});
+
 app.on('window-all-closed', () => {
   // Respect the OSX convention of having the application in memory even
   // after all windows have been closed