[4.2] Fix deprecated warnings in System - Privacy Consent plugin

[joomdonation]

Pull Request for Issue #39468.

Summary of Changes

This PR fixes some deprecated warnings in System - Privacy Consent plugin as described in issue #39468.

Testing Instructions

1. Enable System - Privacy Consent plugin
2. Go to System -> Global Configuration, set Error Reporting to Maximum
3. Login to frontend of your site

Actual result BEFORE applying this Pull Request

You see many deprecated warnings like:

Deprecated: substr(): Passing null to parameter #1 ($string) of type string is deprecated in/home/…/plugins/system/privacyconsent/privacyconsent.php on line 304

Deprecated: substr(): Passing null to parameter #1 ($string) of type string is deprecated in/home/…/plugins/system/privacyconsent/privacyconsent.php on line 305

Deprecated: substr(): Passing null to parameter #1 ($string) of type string is deprecated in/home/…/plugins/system/privacyconsent/privacyconsent.php on line 306

Deprecated: substr(): Passing null to parameter #1 ($string) of type string is deprecated in/home/…/plugins/system/privacyconsent/privacyconsent.php on line 307

Expected result AFTER applying this Pull Request

No warnings anymore.

Link to documentations

Please select:

• No documentation changes for docs.joomla.org needed
• No documentation changes for manual.joomla.org needed

[chmst]

I have tested this item ✅ successfully on 0335db0

code review

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/39475.}

[viocassel]

I have tested this item ✅ successfully on 0335db0

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/39475.}

[Quy]

RTC

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/39475.}

[roland-d]

Thank you.