Electron: Use-after-free in download save dialog callback

Electron is a framework for writing cross-platform desktop applications using JavaScript, HTML and CSS. Prior to versions 38.8.6, 39.8.0, 40.7.0, and 41.0.0-beta.8, apps that allow downloads and programmatically destroy sessions may be vulnerable to a use-after-free. If a session is torn down while a native save-file dialog is open for a download, dismissing the dialog dereferences freed memory, which may lead to a crash or memory corruption. Apps that do not destroy sessions at runtime, or that do not permit downloads, are not affected. This issue has been patched in versions 38.8.6, 39.8.0, 40.7.0, and 41.0.0-beta.8.