Prevent a situation whereby a session-store can somehow end up with n…

…o perWindowState[].closedFrames property, which would then cause the app never recover, even after restart.

Fix #13261, although since that's not reproducible I'm not sure the moving-tab keyboard shortcut neccessarily caused it, but something did, and this will allow recovery in that situation.

js/stores/appStore.js

@@ -309,7 +309,7 @@ const handleAppAction = (action) => {
         break
       }
     case appConstants.APP_SHOW_NOTIFICATION:
-      let notifications = appState.get('notifications')
+      let notifications = appState.get('notifications', Immutable.List())
       notifications = notifications.filterNot((notification) => {
         let message = notification.get('message')
         // action.detail is a regular mutable object only when running tests
@@ -340,7 +340,7 @@ const handleAppAction = (action) => {
       appState = appState.set('notifications', notifications)
       break
     case appConstants.APP_HIDE_NOTIFICATION:
-      appState = appState.set('notifications', appState.get('notifications').filterNot((notification) => {
+      appState = appState.set('notifications', appState.get('notifications', Immutable.List()).filterNot((notification) => {
         return notification.get('message') === action.message
       }))
       break
@@ -355,7 +355,7 @@ const handleAppAction = (action) => {
         const tabsInOrigin = tabState.getTabs(appState).find((tabValue) =>
           urlUtil.getOrigin(tabValue.get('url')) === origin && tabValue.get('tabId') !== immutableAction.get('tabId'))
         if (!tabsInOrigin) {
-          appState = appState.set('notifications', appState.get('notifications').filterNot((notification) => {
+          appState = appState.set('notifications', appState.get('notifications', Immutable.List()).filterNot((notification) => {
             return notification.get('frameOrigin') === origin
           }))
         }

js/stores/windowStore.js

@@ -348,7 +348,7 @@ const doAction = (action) => {
         windowState = windowState.set('closedFrames', new Immutable.List())
       } else {
         windowState = windowState.set('closedFrames',
-          windowState.get('closedFrames').filterNot((frame) => frame.get('location') === action.location))
+          windowState.get('closedFrames', Immutable.List()).filterNot((frame) => frame.get('location') === action.location))
       }
       break
     case windowConstants.WINDOW_SET_PREVIEW_TAB_PAGE_INDEX: