Fixed NRE when setting text on Wide tile only via TileContentBuilder

[supermartzin]

Fixes #3955

PR Type

What kind of change does this PR introduce?

• Bugfix
• Unit test added

What is the current behavior?

Issue #3955

What is the new behavior?

Text on Wide tile is correctly set without throwing NullReferenceException.

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Pull Request has been submitted to the documentation repository instructions. Link:
• Sample in sample app has been added / updated (for bug fixes / features)
  • Icon has been created (if new sample) following the Thumbnail Style Guide and templates
• New major technical changes in the toolkit have or will be added to the Wiki e.g. build changes, source generators, testing infrastructure, sample creation changes, etc...
• Tests for the changes have been added (for bug fixes / features) (if applicable)
• Header has been added to all new source files (run build/UpdateHeaders.bat)
• Contains NO breaking changes

Other information

[ghost]

Thanks supermartzin for opening a Pull Request! The reviewers will test the PR and highlight if there is any conflict or changes required. If the PR is approved we will proceed to merge the pull request 🙌

[net-foundation-cla]

All CLA requirements met.

[net-foundation-cla]

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[michael-hawker]

Thanks @supermartzin! @andrewleader want to take a quick look?

[andrewleader]

Looks great! Thank you @supermartzin!

[ghost]

Hello @michael-hawker!

Because this pull request has the auto merge :zap: label, I will be glad to assist with helping to merge this pull request once all check-in policies pass.

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