Fix submitting forms with empty repeatable subforms

[SharkyKZ]

Summary of Changes

Fixes a regression not allowing to submit forms containing repeatable subforms without any rows added.

Testing Instructions

Try to save Users component or System - Redirect plugin configuration.

Expected result

Form is saved.

Actual result

Validation errors:

Field required: Domain Name
Field required: Term

Documentation Changes Required

No.

[Quy]

I have tested this item ✅ successfully on 59fed21

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/27999.}

[jwaisner]

I have tested this item ✅ successfully on 59fed21

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/27999.}

[jwaisner]

RTC

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/27999.}

[HLeithner]

Thanks