Arbitrary file read via window-open IPC in Electron

In Electron before versions 7.2.4, 8.2.4, and 9.0.0-beta21, arbitrary local file read is possible by defining unsafe window options on a child window opened via window.open. As a workaround, ensure you are calling `event.preventDefault()` on all new-window events where the `url` or `options` is not something you expect. This is fixed in versions 9.0.0-beta.21, 8.2.4 and 7.2.4.