8355415: RichTextArea: NPE in VFlow::scrollCaretToVisible

[andy-goryachev-oracle]

Fixed an NPE that should only happen in a headless test environment.

This is a follow-up for #1677

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Progress

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Issue

• JDK-8355415: RichTextArea: NPE in VFlow::scrollCaretToVisible (Bug - P4)

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• 00: Full (4dc2ad46)