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
}
void Ws::SendInputEvent(v8::Isolate* isolate,
                                 v8::Local<v8::Value> input_event) {
  content::RenderWidgetHostView* view =
      ontents()->GetRenderWidgetHostView();
  if (!view)
    return;
  content::RenderWidgetHost* rwh = view->GetRenderWidgetHost();
  blink::WebInputEvent::Type type =
      gin::GetWebInputEventType(isolate, input_event);
  if (blink::WebInputEvent::IsMouseEventType(type)) {
    blink::WebMouseEvent mouse_event;
    if (gin::ConvertFromV8(isolate, input_event, &mouse_event)) {
      if (IsOffScreen()) {
#if BUILDFLAG(ENABLE_OSR)
        GetOffScreenRenderWidgetHostView()->SendMouseEvent(mouse_event);
#endif
      } else {
        rwh->ForwardMouseEvent(mouse_event);
      }
      return;
    }
  } else if (blink::WebInputEvent::IsKeyboardEventType(type)) {
    content::NativeWebKeyboardEvent keyboard_event(
        blink::WebKeyboardEvent::kRawKeyDown,
        blink::WebInputEvent::kNoModifiers, ui::EventTimeForNow());
    if (gin::ConvertFromV8(isolate, input_event, &keyboard_event)) {
      rwh->ForwardKeyboardEvent(keyboard_event);
      return;
    }