Fix lesson bulk edit

[merkushin]

Resolves #6992

I suppose something has changed in how the form works a few years ago. Updated the processing of data.

Proposed Changes

• Fix lesson bulk edit.

Testing Instructions

1. Create a lesson.
2. Create a few lessons without assigning them to a course.
3. Open lesson list in WP admin, check lessons and choose Edit as a bulk action, then Apply.
4. Update Sensei specific properties (you can test WP properties as well, they are managed by WP), click Update.
5. Make sure lessons have updated data.

Pre-Merge Checklist

• PR title and description contain sufficient detail and accurately describe the changes
• Acceptance criteria is met
• Decisions are publicly documented
• Adheres to coding standards (PHP, JavaScript, CSS, HTML)
• All strings are translatable (without concatenation, handles plurals)
• Follows our naming conventions (P6rkRX-4oA-p2)
• Hooks (p6rkRX-1uS-p2) and functions are documented
• New UIs are responsive and use a mobile-first approach
• New UIs match the designs
• Different user privileges (admin, teacher, subscriber) are tested as appropriate
• Legacy courses (course without blocks) are tested
• Code is tested on the minimum supported PHP and WordPress versions
• User interface changes have been tested on the latest versions of Chrome, Firefox and Safari
• "Needs Documentation" label is added if this change requires updates to documentation
• Known issues are created as new GitHub issues

[codecov]

Codecov Report

Attention: Patch coverage is 4.54545% with 21 lines in your changes are missing coverage. Please review.

Project coverage is 51.50%. Comparing base (c39ebf7) to head (8f50047).
Report is 1 commits behind head on trunk.

Additional details and impacted files

@@             Coverage Diff              @@
##              trunk    #7515      +/-   ##
============================================
- Coverage     51.51%   51.50%   -0.01%     
  Complexity    11231    11231              
============================================
  Files           622      622              
  Lines         47505    47511       +6     
  Branches        414      414              
============================================
  Hits          24471    24471              
- Misses        22701    22707       +6     
  Partials        333      333              

Files	Coverage Δ
includes/class-sensei-lesson.php	35.96% <4.54%> (-0.09%)	⬇️

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[renatho]

Works well for me!

[Imran92]

Works as expected! 👍 👍 Just left a comment about a possible logic check change.

Also, do you think we should add an integration test here to make sure that if it breaks for some reason, we'll know? Because in this case, we didn't know how long it was broken for or what broke it. Having an integration test saving these meta fields can potentially save us from these scenarios I think

[Imran92]

Probably assigning to the empty array here is not necessary, because we already checked if it is an array on line 4337

[merkushin]

Thanks, @Imran92! You're right. I'll create a separate PR with a test for it.
Just want to include this fix into our alpha release.

[Imran92]

Added a comment about a performance concern here #7523 (comment)