Fixes #6690 Prevent type error if preg_replace() returns null

[Tabrisrp]

Description

Fixes #6690

Documentation

Technical documentation

preg_replace can return null` when there is an error, and if we use the value after, it will cause a fatal error due to passing an incorrect type.

Adding a guard clause prevents the issue.

Type of change

• Bug fix (non-breaking change which fixes an issue).

Checklists

Feature validation

• I validated all the Acceptance Criteria. If possible, provide sreenshots or videos.
• I triggered all changed lines of code at least once without new errors/warnings/notices.
• I implemented built-in tests to cover the new/changed code.

Code style

• I wrote self-explanatory code about what it does.
• I wrote comments to explain why it does it.
• I named variables and functions explicitely.
• I protected entry points against unexpected inputs.
• I did not introduce unecessary complexity.

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
Report missing for 60749b71	✅ 66.67% (target: 50.00%)

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (60749b7)	Report Missing	Report Missing	Report Missing
Head commit (cb8762c)	37239	14403	38.68%

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#6691)	6	4	66.67%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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Footnotes

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[hanna-meda]

As the error is hard to trigger, we ran a smoke test on preloading LCP + clear critical images. No error was encountered.
We'll monitor this also during Test Run execution for 3.16.1 prerelease.