fix: null check before accessing dsl of page in getCurrentPageWidgets selector (#28572)

#### PR fixes following issue(s)
Fixes https://github.com/appsmithorg/appsmith/issues/28373

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

## Testing
>
#### How Has This Been Tested?
> Please describe the tests that you ran to verify your changes. Also
list any relevant details for your test configuration.
> Delete anything that is not relevant
- [x] Manual
- [ ] JUnit
- [ ] Jest
- [ ] Cypress
>
>
#### Test Plan
> Add Testsmith test cases links that relate to this PR
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>
#### 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
- [x] My code follows the style guidelines of this project
- [x] 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
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [x] 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/selectors/entitiesSelector.ts

@@ -709,7 +709,9 @@ export const getCurrentPageWidgets = createSelector(
   getPageWidgets,
   getCurrentPageId,
   (widgetsByPage, currentPageId) =>
-    currentPageId ? widgetsByPage[currentPageId].dsl : {},
+    currentPageId && widgetsByPage[currentPageId]
+      ? widgetsByPage[currentPageId].dsl
+      : {},
 );
 
 export const getParentModalId = (