Fix issue 8403 ([C++] : Issue with generated code when naked buffer on a field)

[nolankramer]

Fixes https://github.com/google/flatbuffers/issues/8403

https://github.com/google/flatbuffers/pull/8286 can be closed.

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[nolankramer]

Can the checks be run on this please? @dbaileychess

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This pull request is stale because it has been open 6 months with no activity. Please comment or label not-stale, or this will be closed in 14 days.

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This pull request was automatically closed due to no activity for 6 months plus the 14 day notice period.