Handle empty handles (#11598)

* Handle empty handles

* Close and dispose window at end of void test

* Dispose of existing window before running void 0 spec

spec/api-browser-window-spec.js

@@ -86,6 +86,16 @@ describe('BrowserWindow module', () => {
     return closeWindow(w).then(() => { w = null })
   })
 
+  describe('BrowserWindow constructor', () => {
+    it('allows passing void 0 as the webContents', () => {
+      w.close()
+      w = null
+      w = new BrowserWindow({
+        webContents: void 0
+      })
+    })
+  })
+
   describe('BrowserWindow.close()', () => {
     let server