Guard for nulls in processors and abort if necessary

[mkevins]

Fixes: #12104

This PR guards for nulls in the processor Json handling. While it isn't clear why ids would not be present in parsed json from the block header, returning false will leave the content unchanged. Since no changes can be made to the parsed structure without matching the id, aborting should be the safest route.

I believe the reason why the id is missing is that it is not present in the templates, though I have not yet confirmed this.

Steps to test

• Install and launch the application
• Tap on "Log In"
• Log in to the app using valid credentials
• Go to My site and tap on "Pages" icon
• Go to Drafts and tap on "CREATE A PAGE" button
• Select the Service template (observe template preview)
• Tap "Apply" option
• Insert Image block
• Add an image with "Choose from device"
• Leave the editor (tap back button) before the upload completes

Expected:

The app should not crash, and upload should complete successfully

• When upload has finished (observed in the notifications) reopen the page
• Switch to HTML view

Expected:

The url for the added image should be a remote URL (i.e. https:// not file://)

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[peril-wordpress-mobile]

You can test the changes on this Pull Request by downloading the APK here.

[peril-wordpress-mobile]

	Warnings
⚠️	PR is not assigned to a milestone.

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[chipsnyder]

Great job tracking that down! Tested the case above and it all worked well.

[mkevins]

Thanks Chip for reviewing and testing so quickly!