! Fix new window not created when all windows closed and app activated (#1203)

Since the app is coded to quit for non MacOS when all windows are closed
This issue happens only on MacOS

src/main/index.js

@@ -423,7 +423,7 @@ function runApp() {
   })
 
   app.on('activate', () => {
-    if (mainWindow === null) {
+    if (mainWindow === null || mainWindow === undefined) {
       createWindow()
     }
   })