fix: If navigation settings object is empty in application details, use the default settings (#27779)

## Description
We removed the clone/duplication feature, but if an app for some reason
has an empty navigation settings object - it doesn't show any pages in
the navbar nor any of the customization options for navigation inside
the app settings pane. This PR adds a check for this and uses the
default navigation settings as a fallback.

#### PR fixes following issue(s)
Fixes #27721
Fixes #23565

#### Type of change
- Bug fix (non-breaking change which fixes an issue)

## Testing

#### How Has This Been Tested?
To recreate this scenario, we can import this app that has an empty
navigation settings object. [App JSON
here.](https://github.com/appsmithorg/appsmith/files/12791775/navigationSettingsEmptyObject.json.zip)

- [x] Manual
- [ ] JUnit
- [ ] Jest
- [ ] Cypress
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#### Test Plan
> Add Testsmith test cases links that relate to this PR
>
>
#### Issues raised during DP testing
> Link issues raised during DP testing for better visiblity and tracking
(copy link from comments dropped on this PR)
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## Checklist:
#### Dev activity
- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my own code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] PR is being merged under a feature flag


#### QA activity:
- [ ] [Speedbreak
features](https://github.com/appsmithorg/TestSmith/wiki/Guidelines-for-test-plans#speedbreakers-)
have been covered
- [ ] Test plan covers all impacted features and [areas of
interest](https://github.com/appsmithorg/TestSmith/wiki/Guidelines-for-test-plans#areas-of-interest-)
- [ ] Test plan has been peer reviewed by project stakeholders and other
QA members
- [ ] Manually tested functionality on DP
- [ ] We had an implementation alignment call with stakeholders post QA
Round 2
- [ ] Cypress test cases have been added and approved by SDET/manual QA
- [ ] Added `Test Plan Approved` label after Cypress tests were reviewed
- [ ] Added `Test Plan Approved` label after JUnit tests were reviewed

app/client/src/ce/reducers/uiReducers/applicationsReducer.tsx

@@ -27,7 +27,7 @@ import type { IconNames } from "design-system";
 import type { NavigationSetting } from "constants/AppConstants";
 import { defaultNavigationSetting } from "constants/AppConstants";
 import produce from "immer";
-import { groupBy } from "lodash";
+import { groupBy, isEmpty } from "lodash";
 
 export const initialState: ApplicationsReduxState = {
   isFetchingApplications: false,
@@ -242,7 +242,10 @@ export const handlers = {
       isFetchingApplication: false,
     };
 
-    if (!newState.currentApplication.applicationDetail.navigationSetting) {
+    if (
+      !newState.currentApplication.applicationDetail.navigationSetting ||
+      isEmpty(newState.currentApplication.applicationDetail.navigationSetting)
+    ) {
       newState.currentApplication.applicationDetail.navigationSetting =
         defaultNavigationSetting;
     }