Fix interstitial not progressing to next task with web entry start events

[sanjacornelius]

Issue & Reproduction Steps

Ticket: FOUR-5414

Web entry Start Event with interstitial screen configured does not progress to the next assigned task. Console error appears Cannot read properties of null (reading 'process_request_id')

1. Create a Web Entry Start Event and configure an interstitial screen.
   
2. Add a form task and enable Web Entry
2. Add end event

3. Save and run the process.

Expected behavior:
When selecting the submit button the interstitial displays then loads the next assigned task.

Actual behavior:
When selecting the submit button the interstitial screen continuously displays and never loads the next assigned task.

Solution

• Check if this.task exists before retrieving the process_request_id key.

How to Test

1. Test the replication steps above.
2. Test the use cases in this PR to ensure the fix for subprocesses isn't broken.

Related Tickets & Packages

Code Review Checklist

• I have pulled this code locally and tested it on my instance, along with any associated packages.
• This code adheres to ProcessMaker Coding Guidelines.
• This code includes a unit test or an E2E test that tests its functionality, or is covered by an existing test.
• This solution fixes the bug reported in the original ticket.
• This solution does not alter the expected output of a component in a way that would break existing Processes.
• This solution does not implement any breaking changes that would invalidate documentation or cause existing Processes to fail.
• This solution has been tested with enterprise packages that rely on its functionality and does not introduce bugs in those packages.
• This code does not duplicate functionality that already exists in the framework or in ProcessMaker.
• This ticket conforms to the PRD associated with this part of ProcessMaker.

[eiresendez]

Hi Sanja - I tested the cases of Pull 1173 and there are conflicts, please watch the next videos for more information:

Testing in bugfix/FOUR-5414 branch:
https://user-images.githubusercontent.com/90741874/154565925-85eb454f-3abc-4201-bd6a-6c9644b8a1a9.mov

Testing in develop branch:
https://user-images.githubusercontent.com/90741874/154565957-bee013b8-ac07-40a1-b0e8-d012e4ea21a7.mov

[eiresendez]

PR's changes correctly fix the issue with Web Entries. The problem I mentioned is not related to these changes.