message: Electron 549: fix main window show javascript error issues
  support not quitting app on mac upon closing window
  add extra checks for showing main window
diff: @@ -679,8 +679,10 @@ function getWindowSizeAndPosition(window) {
  * Shows the main window
  */
  function showMainWindow() {
  + if (mainWindow) {
  mainWindow.show();
  }
  +}
  /**
  * Tells if a window is the main window
  