[4.4] Contact VCF: Properly assign value to array

[Hackwar]

Summary of Changes

While going through the code with phpstan, this showed up as error. Instead of assigning the string to a new entry in the array, we are also trying to read from this array by trying to concatenate a string... I'm struggling to explain it, but if you look at the code, you see the problem. Right now this does not throw an error in PHP, but it is just a matter of time when PHP becomes strict enough to complain about this.

Testing Instructions

Codereview

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

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[HLeithner]

code review

[Quy]

I have tested this item ✅ successfully on 59e7346

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[Quy]

RTC

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/43353.}

[MacJoom]

Thank you!