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
if (path.empty()) {
    args->ThrowError("path cannot be empty");
    return;
  }
  DevToolsRemoveFileSystem(path);
}
void Ws::Undo() {
  ontents()->Undo();
}
void Ws::Redo() {
  ontents()->Redo();
}
void Ws::Cut() {
  ontents()->Cut();
}
void Ws::Copy() {
  ontents()->Copy();
}
void Ws::Paste() {
  ontents()->Paste();
}
void Ws::PasteAndMatchStyle() {
  ontents()->PasteAndMatchStyle();
}
void Ws::Delete() {
  ontents()->Delete();
}
void Ws::SelectAll() {
  ontents()->SelectAll();
}