[6.0] Fix frontend save template options error

[joomdonation]

Pull Request for Issue # .

Summary of Changes

This PR fixes fatal error when saving template options from frontend.

Testing Instructions

• Use Joomla 6.0 nightly build
• Create a menu item to link to Configuration -> Display Template Options menu item type
• Login to frontend of your site using super user accountt
• Access to the above menu item and try to change template options, save it

Actual result BEFORE applying this Pull Request

You got fatal error

Expected result AFTER applying this Pull Request

No error, template options saved properly

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

[exlemor]

I have tested this item ✅ successfully on ccc73d1

Another quick and clear test - I was able to test this successfully.

Thanks @joomdonation.

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[krishnaGandhi11]

I have tested this item ✅ successfully on ccc73d1

Tested Successfully! @joomdonation .

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[QuyTon]

RTC

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