Electron Version: 7.1.1
Operating System: Windows 10 (1803)

If I set the 'margins' option when call webContents.print method,
The app will crash with no error message.

```js
let { remote } = require("electron");
let webContents = remote.getCurrentWebContents();
webContents.print(
  {
    margins: {
      marginType: "custom",
      top: 30,
      bottom: 0,
      left: 0,
      right: 0
    }
  },
  (success, errorType) => {
    if (!success) console.log(errorType);
  }
);
```

shell/browser/api/electron_api_web_contents.cc
v8::Isolate* isolate,
    std::unique_ptr<content::Ws> owned_ontents,
    gin::Handle<api::Session> session,
    const gin_helper::Dictionary& options) {
  Observe(owned_ontents.get());
  
  
  
  InitWithWs(owned_ontents.release(), session->browser_context(),
                      IsGuest());
  managed_ontents()->GetView()->SetDelegate(this);
  auto* prefs = ontents()->GetMutableRendererPrefs();
  prefs->accept_languages = g_browser_process->GetApplicationLocale();
#if defined(OS_LINUX) || defined(OS_WIN)
  
  static const base::NoDestructor<gfx::FontRenderParams> params(
      gfx::GetFontRenderParams(gfx::FontRenderParamsQuery(), nullptr));
  prefs->should_antialias_text = params->antialiasing;
  prefs->use_subpixel_positioning = params->subpixel_positioning;
  prefs->hinting = params->hinting;
  prefs->use_autohinter = params->autohinter;
  prefs->use_bitmaps = params->use_bitmaps;
  prefs->subpixel_rendering = params->subpixel_rendering;
#endif
  
  if (auto interval = GetCursorBlinkInterval())
    prefs->caret_blink_interval = *interval;
  
  new WsPreferences(ontents(), options);
  WsPermissionHelper::CreateForWs(ontents());