Use continue instead of return when bulk tracking pixel processing

[claudiulodro]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

Currently the function that records log views uses a return if it encounters an invalid newsletter tracking ID. When that happens, all of the other events after it in the list get thrown away and are not tracked. Using break is better IMO, so any valid events after the invalid one get processed.

How to test the changes in this Pull Request:

Not sure, but I encountered it in the wild. Something like this:

1. Have a log file with multiple newsletter's tracking pixels.
2. Manually delete or change the tracking ID meta on one of the newsletters, so the check fails.
3. wp shell and Newspack_Newsletters\Tracking\Pixel::process_logs()
4. Observe the data for events after the invalid newsletter isn't recorded.

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 24.80%. Comparing base (707891c) to head (3e92957).
⚠️ Report is 7 commits behind head on trunk.

Files with missing lines	Patch %	Lines
includes/tracking/class-pixel.php	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##              trunk    #1961   +/-   ##
=========================================
  Coverage     24.80%   24.80%           
  Complexity     2926     2926           
=========================================
  Files            50       50           
  Lines         10355    10355           
=========================================
  Hits           2569     2569           
  Misses         7786     7786           

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